Merge bitcoin/bitcoin#33888: ci: Re-enable LINT_CI_SANITY_CHECK_COMMIT_SIG

55555db055 doc: Add missing --platform=linux to docker build command (MarcoFalke)
fa0ce4c148 ci: Re-enable LINT_CI_SANITY_CHECK_COMMIT_SIG (MarcoFalke)
faa0973de2 ci: [refactor] Rename CIRRUS_PR env var to LINT_CI_IS_PR (MarcoFalke)
fa1dacaebe ci: Move lint exec snippet to stand-alone py file (MarcoFalke)

Pull request description:

  The sanity check to check the last few merge commit signatures on the main branch was accidentally and silently disabled while moving from the `cirrus-ci.com` platform to the GHA platform.

  So fix that by re-enabling it.

  Also, contains a few other lint cleanup commits.

ACKs for top commit:
  janb84:
    re ACK 55555db055
  willcl-ark:
    ACK 55555db055

Tree-SHA512: e623dc88035ee4d1c6a8efa5fad33c35cface87f54e78c7ebfe5d468d28d8d8097150344d276f90f8ed52a89e61609ce95380476ea0151b50f73ad5919233933

.github/workflows/ci.yml

@@ -621,40 +621,4 @@ jobs:
           cache-provider: ${{ needs.runners.outputs.provider }}
 
       - name: CI script
-        shell: python
-        run: |
-          import os, shlex, subprocess, sys, time
-
-          def run(cmd, **kwargs):
-              print("+ " + shlex.join(cmd), flush=True)
-              kwargs.setdefault("check", True)
-              try:
-                  return subprocess.run(cmd, **kwargs)
-              except Exception as e:
-                  sys.exit(e)
-
-          CONTAINER_NAME = os.environ["CONTAINER_NAME"]
-
-          build_cmd = [
-              "docker", "buildx", "build",
-              f"--tag={CONTAINER_NAME}",
-              *shlex.split(os.getenv("DOCKER_BUILD_CACHE_ARG", "")),
-              "--file=./ci/lint_imagefile",
-              "."
-          ]
-
-          if run(build_cmd, check=False).returncode != 0:
-              print("Retry building image tag after failure")
-              time.sleep(3)
-              run(build_cmd)
-
-          CIRRUS_PR_FLAG = []
-          if '${{ github.event_name }}' == "pull_request":
-              CIRRUS_PR_FLAG = ["-e", "CIRRUS_PR=1"]
-
-          run([
-              "docker", "run", "--rm",
-              *CIRRUS_PR_FLAG,
-              f"--volume={os.getcwd()}:/bitcoin",
-              CONTAINER_NAME,
-          ])
+        run: python .github/ci-lint-exec.py