[BE] Add script to keept the runner-determinator scripts in sync (#136794)

Whenever we update runner_determinator.py it needs to be copied over into _runner-determinator.yml.

This is a quick utility script to make that process less tedious
Pull Request resolved: https://github.com/pytorch/pytorch/pull/136794
Approved by: https://github.com/zxiiro, https://github.com/jeanschmidt

.github/scripts/runner_determinator.py

@@ -1,5 +1,9 @@
 # flake8: noqa: G004
 
+# Note: Copies of this script in runner_determinator.py and _runner-determinator.yml
+#       must be kept in sync. You can do it easily by running the following command:
+#           python .github/scripts/update_runner_determinator.py
+
 """
 This runner determinator is used to determine which set of runners to run a
 GitHub job on. It uses the first comment of a GitHub issue (by default

.github/scripts/update_runner_determinator.py

@@ -0,0 +1,31 @@
+#!/usr/bin/env python3
+
+import re
+
+
+# Read the contents of runner_determinator.py
+with open(".github/scripts/runner_determinator.py") as script_file:
+    script_content = script_file.read()
+
+# Indent the script content by 10 spaces to match destination indentation
+indented_script_content = "\n".join(
+    [" " * 10 + line if line else line for line in script_content.splitlines()]
+)
+
+# Read the contents of _runner-determinator.yml
+with open(".github/workflows/_runner-determinator.yml") as yml_file:
+    yml_content = yml_file.read()
+
+# Replace the content between the markers
+new_yml_content = re.sub(
+    r"(cat <<EOF > runner_determinator.py\n)(.*?)(\n\s+EOF)",
+    lambda match: match.group(1) + indented_script_content + match.group(3),
+    yml_content,
+    flags=re.DOTALL,
+)
+
+# Save the modified content back to _runner-determinator.yml
+with open(".github/workflows/_runner-determinator.yml", "w") as yml_file:
+    yml_file.write(new_yml_content)
+
+print("Updated _runner-determinator.yml with the contents of runner_determinator.py")

.github/workflows/_runner-determinator.yml

@@ -59,6 +59,10 @@ jobs:
           cat <<EOF > runner_determinator.py
           # flake8: noqa: G004
 
+          # Note: Copies of this script in runner_determinator.py and _runner-determinator.yml
+          #       must be kept in sync. You can do it easily by running the following command:
+          #           python .github/scripts/update_runner_determinator.py
+
           """
           This runner determinator is used to determine which set of runners to run a
           GitHub job on. It uses the first comment of a GitHub issue (by default