Merge bitcoin/bitcoin#28279: ci: Add test-each-commit task

fa5356c ci: Limit test-each-commit to --max-count=6 (MarcoFalke)
fafcd2e ci: Add test-each-commit task (MarcoFalke)

Pull request description:

  Currently, if a pull request has more than one commit, previous commits may fail to compile, or may fail the tests. This is problematic, because it breaks git-bisect, or worse.

  Fix this by adding a CI task for this.

ACKs for top commit:
  jonatack:
    ACK fa5356c
  dergoegge:
    utACK fa5356c
  hebasto:
    ACK fa5356c

Tree-SHA512: 304eff5545501ee499b881f0b0a0c1fe32a7c9f00d96b45bba731af08ac5ca917cef223f5c3d346e30c11a3e6e12e1da297929d3caea9644f3ec1de25dd97c37

.github/workflows/ci.yml

@@ -23,6 +23,23 @@ env:
   MAKEJOBS: '-j10'
 
 jobs:
+  test-each-commit:
+    name: 'test each commit'
+    runs-on: ubuntu-22.04
+    if: github.event_name == 'pull_request'
+    timeout-minutes: 360  # Use maximum time, see https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idtimeout-minutes. Assuming a worst case time of 1 hour per commit, this leads to a --max-count=6 below.
+    env:
+      MAX_COUNT: '--max-count=6'
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+          fetch-depth: '8'  # Two more than $MAX_COUNT
+      - run: git checkout HEAD~  # Skip the top commit, because it is already checked by the other tasks.
+      - run: sudo apt install clang ccache build-essential libtool autotools-dev automake pkg-config bsdmainutils python3-zmq libevent-dev libboost-dev libsqlite3-dev libdb++-dev systemtap-sdt-dev libminiupnpc-dev libnatpmp-dev libqt5gui5 libqt5core5a libqt5dbus5 qttools5-dev qttools5-dev-tools qtwayland5 libqrencode-dev -y
+      # Use clang++, because it is a bit faster and uses less memory than g++
+      - run: git rebase --exec "echo Running test-one-commit on \$( git log -1 ) && ./autogen.sh && CC=clang CXX=clang++ ./configure && make clean && make -j $(nproc) check && ./test/functional/test_runner.py -j $(( $(nproc) * 2 ))" "$( git log '^'$( git log --merges -1 --format='%H' ) HEAD --format='%H' ${MAX_COUNT} | tail -1 )~1"
+
   macos-native-x86_64:
     name: 'macOS 13 native, x86_64, no depends, sqlite only, gui'
     # Use latest image, but hardcode version to avoid silent upgrades (and breaks).