fix(ci): cut-release tombstone sync handles no-op substitution

The 'Sync plugin versions' step has two Python heredocs that rewrite
the version in tombstones/pypi/pyproject.toml and the heading in
tombstones/vscode/CHANGELOG.md. Both used 'if new_t == t' as the
sanity guard, which incorrectly fired whenever the substitution was
a byte-identical no-op — exactly what happens when the file is
authored directly at the target version (as the tombstones were for
v0.3.0 in PR #186).

Replace the post-substitution equality check with an explicit
pre-substitution anchor-presence check:

    if not re.search(PATTERN, t, flags=re.MULTILINE):
        raise SystemExit('::error::... anchor not found.')
    new_t = re.sub(PATTERN, ..., t, count=1, flags=re.MULTILINE)
    p.write_text(new_t, ...)

This correctly distinguishes 'regex anchor missed' (real bug; fail)
from 'anchor matched, value already at target' (legitimate; no-op
write is harmless because the workflow's downstream Update CHANGELOG
step always mutates CHANGELOG.md so the resulting commit is non-empty).

Failure surfaced by run 26608283472 (v0.3.0 first dispatch); the
release branch was not pushed because the failure happened before
Commit and push.

Author: Dongbumlee

.github/workflows/cut-release.yml

@@ -125,9 +125,10 @@ jobs:
           v = os.environ["VERSION"]
           p = pathlib.Path("tombstones/pypi/pyproject.toml")
           t = p.read_text(encoding="utf-8")
-          new_t = re.sub(r'^version = "[^"]+"', f'version = "{v}"', t, count=1, flags=re.MULTILINE)
-          if new_t == t:
-              raise SystemExit("::error::tombstones/pypi/pyproject.toml version was not updated; check the regex anchor.")
+          PATTERN = r'^version = "[^"]+"'
+          if not re.search(PATTERN, t, flags=re.MULTILINE):
+              raise SystemExit("::error::tombstones/pypi/pyproject.toml version regex anchor not found.")
+          new_t = re.sub(PATTERN, f'version = "{v}"', t, count=1, flags=re.MULTILINE)
           p.write_text(new_t, encoding="utf-8")
           PY
           echo "tombstones/pypi/pyproject.toml → $VERSION"
@@ -138,13 +139,10 @@ jobs:
           v = os.environ["VERSION"]
           p = pathlib.Path("tombstones/vscode/CHANGELOG.md")
           text = p.read_text(encoding="utf-8")
-          new_text = re.sub(
-              r"^## \[\d+\.\d+\.\d+\] - (?:YYYY-MM-DD|\d{4}-\d{2}-\d{2})",
-              f"## [{v}] - YYYY-MM-DD",
-              text, count=1, flags=re.MULTILINE,
-          )
-          if new_text == text:
-              raise SystemExit("::error::tombstones/vscode/CHANGELOG.md heading was not updated; check the regex anchor.")
+          PATTERN = r"^## \[\d+\.\d+\.\d+\] - (?:YYYY-MM-DD|\d{4}-\d{2}-\d{2})"
+          if not re.search(PATTERN, text, flags=re.MULTILINE):
+              raise SystemExit("::error::tombstones/vscode/CHANGELOG.md heading regex anchor not found.")
+          new_text = re.sub(PATTERN, f"## [{v}] - YYYY-MM-DD", text, count=1, flags=re.MULTILINE)
           p.write_text(new_text, encoding="utf-8")
           PY
           echo "tombstones/vscode/CHANGELOG.md → [$VERSION] (date sentinel preserved)"