Merge bitcoin/bitcoin#34136: test: Allow mempool_updatefromblock.py to run on 32-bit

fac5a1b10a test: Allow mempool_updatefromblock.py to run on 32-bit (MarcoFalke)

Pull request description:

  The number of dropped parent transactions in the `test_max_disconnect_pool_bytes` test was hard-coded to `2`.

  This happens to work fine on 64-bit for now. However, it seems to fail on 32-bit (https://github.com/bitcoin/bitcoin/issues/34108).

  I don't think we care about the exact number, as long as it is at least `1`.

  So hard-code `1` for an initial sanity check, and then calculate the exact value at runtime via `len(mempool) // 2`.

  Also, enable the functional tests in 32-bit CI, to confirm the regression test.

  Fixes https://github.com/bitcoin/bitcoin/issues/34108

ACKs for top commit:
  bensig:
    ACK fac5a1b10a
  instagibbs:
    ACK fac5a1b10a

Tree-SHA512: 8d468f306d95e52cbfac1803293e3b8e9575c9010200010c7833382112509e0d51827dc9681b0b68eeae742af2c14d12da5fd4cf0e1d871a02f91fc80e6720d1

ci/test/00_setup_env_arm.sh

@@ -12,8 +12,6 @@ export PACKAGES="python3-zmq g++-arm-linux-gnueabihf libc6:armhf libstdc++6:armh
 export CONTAINER_NAME=ci_arm_linux
 export CI_IMAGE_NAME_TAG="mirror.gcr.io/ubuntu:24.04"  # Check that https://packages.ubuntu.com/noble/g++-arm-linux-gnueabihf (version 13.x, similar to guix) can cross-compile
 export CI_IMAGE_PLATFORM="linux/arm64"
-export RUN_UNIT_TESTS=true
-export RUN_FUNCTIONAL_TESTS=false
 export GOAL="install"
 export CI_LIMIT_STACK_SIZE=1
 # -Wno-psabi is to disable ABI warnings: "note: parameter passing for argument of type ... changed in GCC 7.1"