altos: FTBFS with OpenJDK 21 due to unsupported javac source/target level 7

Dear Maintainers,

The package altos ftbfs with default Java 21.
The relevant part of the build log:
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make[3]: Entering directory '/<<PKGBUILDDIR>>/altoslib'
mkdir -p bin; CLASSPATH=bin /usr/lib/jvm/default-java/bin/javac -d bin -target 1.7 -source 1.7 -encoding UTF-8 -Xlint:deprecation -Xlint:unchecked AltosLib.java AltosAccelCal.java AltosAccelCalListener.java AltosAdxl375.java AltosCalData.java AltosCompanion.java AltosConfigData.java AltosConfigDataException.java AltosConfigValues.java AltosConvert.java AltosCRCException.java AltosCSV.java AltosDebug.java AltosEeprom.java AltosRecordSet.java AltosEepromRecord.java AltosEepromRecordFull.java AltosEepromRecordTiny.java AltosEepromRecordMega.java AltosEepromRecordMetrum.java AltosEepromRecordMini.java AltosEepromRecordGps.java AltosEepromRecordFireTwo.java AltosEepromRecordMicroPeak2.java AltosEepromRecordMotor.java AltosEepromRecordSet.java AltosEepromChunk.java AltosEepromDownload.java AltosEepromMonitor.java AltosEepromFile.java AltosEepromList.java AltosEepromLog.java AltosFile.java AltosFilterListener.java AltosFlash.java AltosFlashListener.java AltosDataListener.java AltosDataProvider.java AltosFlightSeries.java AltosFlightReader.java AltosFlightStats.java AltosForce.java AltosFrequency.java AltosGPS.java AltosGPSTimeValue.java AltosGPSSat.java AltosGauss.java AltosGreatCircle.java AltosHexfile.java AltosHexsym.java AltosIdle.java AltosIdleFetch.java AltosIdleMonitor.java AltosIdleMonitorListener.java AltosIdleReader.java AltosIgnite.java AltosIMU.java AltosKML.java AltosLine.java AltosLink.java AltosListenerState.java AltosLog.java AltosLogTrace.java AltosMag.java AltosMma655x.java AltosMs5607.java AltosNoSymbol.java AltosOrient.java AltosParse.java AltosPressure.java AltosPresTemp.java AltosPreferences.java AltosPreferencesBackend.java AltosProgrammer.java AltosPyroName.java AltosReplayReader.java AltosRomconfig.java AltosSavedState.java AltosSelfFlash.java AltosUsbId.java AltosSensorMM.java AltosSensorEMini.java AltosSensorEasyTimer1.java AltosSensorTM.java AltosSensorTMini2.java AltosSensorTMini3.java AltosSensorMega.java AltosSensorMetrum.java AltosSensorTGPS1.java AltosSensorTGPS2.java AltosSensorTGPS3.java AltosSensorEasyMotor2.java AltosState.java AltosStateName.java AltosStringInputStream.java AltosTelemetry.java AltosTelemetryConfiguration.java AltosTelemetryCompanion.java AltosTelemetryFile.java AltosTelemetryIterable.java AltosTelemetryLegacy.java AltosTelemetryLocation.java AltosTelemetryMap.java AltosTelemetryMegaSensor.java AltosTelemetryMegaNorm.java AltosTelemetryMegaData.java AltosTelemetryMini2.java AltosTelemetryMini3.java AltosTelemetryMetrumSensor.java AltosTelemetryMetrumData.java AltosTelemetryReader.java AltosTelemetryRaw.java AltosTelemetrySensor.java AltosTelemetrySatellite.java AltosTelemetryStandard.java AltosTime.java AltosTimeSeries.java AltosTimeValue.java AltosUnitsListener.java AltosUnknownProduct.java AltosUnits.java AltosUnitsRange.java AltosDistance.java AltosHeight.java AltosSpeed.java AltosTemperature.java AltosAccel.java AltosVoltage.java AltosLocation.java AltosLatitude.java AltosLongitude.java AltosRotationRate.java AltosPyro.java AltosWriter.java AltosQuaternion.java AltosRotation.java AltosImage.java AltosLatLon.java AltosMap.java AltosMapCache.java AltosMapCacheListener.java AltosMapInterface.java AltosMapLine.java AltosMapMark.java AltosMapPath.java AltosMapPathPoint.java AltosMapRectangle.java AltosMapStore.java AltosMapStoreListener.java AltosMapTile.java AltosMapTileListener.java AltosMapTransform.java AltosMapZoomListener.java AltosPointDouble.java AltosPointInt.java AltosRectangle.java AltosFlightDisplay.java AltosFontListener.java AltosLaunchSite.java AltosLaunchSiteListener.java AltosLaunchSites.java AltosMapLoaderListener.java AltosMapLoader.java AltosMapTypeListener.java AltosJson.java AltosVersion.java AltosUnitInfo.java AltosUnitInfoListener.java
warning: [options] bootstrap class path not set in conjunction with -source 7
error: Source option 7 is no longer supported. Use 8 or later.
error: Target option 7 is no longer supported. Use 8 or later.
make[3]: *** [Makefile:523: classaltoslib.stamp] Error 2
make[3]: Leaving directory '/<<PKGBUILDDIR>>/altoslib'
make[2]: *** [Makefile:500: all-recursive] Error 1
make[2]: Leaving directory '/<<PKGBUILDDIR>>'
make[1]: *** [Makefile:424: all] Error 2
make[1]: Leaving directory '/<<PKGBUILDDIR>>'
make: *** [debian/rules:28: build-stamp] Error 2
dpkg-buildpackage: error: debian/rules build-arch subprocess returned exit status 2
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Build finished at 2023-05-04T13:23:52Z
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