ci: Move lint exec snippet to stand-alone py file

Moving the python code out of the yaml string makes it easier to lint,
format, and edit.

This can be reviewed with the git options:

--color-moved=dimmed-zebra --color-moved-ws=ignore-all-space

.github/ci-lint-exec.py

@@ -0,0 +1,51 @@
+#!/usr/bin/env python3
+# Copyright (c) The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or https://opensource.org/license/mit.
+
+import os
+import shlex
+import subprocess
+import sys
+import 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)
+
+
+def main():
+    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 os.environ.get("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,
+    ])
+
+
+if __name__ == "__main__":
+    main()

.github/workflows/ci.yml

@@ -620,40 +620,4 @@ 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