Removing irqbalance disables power button on Raspberry Pi 5

As discussed in Bug #1833322: "Please consider no more having irqbalance enabled by default (per image/use-case/TBD)" (https://bugs.launchpad.net/ubuntu/+source/ubuntu-meta/+bug/1833322) the irqbalance package will no longer be installed by default in Noble. So as a test I removed the package from my Raspberry Pi 5 running Mantic Server, after which the Pi 5's power button no longer worked to poweroff the system. Re-installing irqbalance caused the button to work again.

With irqbalance installed I see these messages at boot time:

kernel: input: pwr_button as /devices/platform/pwr_button/input/input1
systemd-logind[694]: Watching system buttons on /dev/input/event0 (pwr_button)

Without irqbalance I see this:

kernel: gpio-keys pwr_button: Unable to get irq number for GPIO 0, error -6

So the Raspberry Pi 5 might still need irqbalance installed, or perhaps there's a better solution for enabling the button.

I have the following appended to the Mantic default /boot/firmware/config.txt:

# Trickle charge the RTC battery (default: don't charge)
dtparam=rtc_bbat_vchg=3000000
# Enable the PCIe external connector
dtparam=nvme
# Force PCIe Gen 3.0 (default: Gen 2.0; not certified for Gen 3.0)
# dtparam=pciex1_gen=3
# Enable second serial port on GPIO 14 & 15 (default: disabled)
dtparam=uart0
# Change activity LED behavior (default: blink for MMC access)
dtparam=act_led_trigger=heartbeat
# Disable Bluetooth (not wanted on a server)
dtoverlay=disable-bt-pi5
# Enable PPS on GPIO 18 for MAX-M8Q GNSS HAT
dtoverlay=pps-gpio,gpiopin=18,capture_clear