fix(vuln): metric label extractor handles escaped quotes in f-strings

Co-Authored-By: Claude Opus 5.5 <[email protected]>

conformance/tests/l0-static/vuln-metrics-no-per-cve-label/check.sh

@@ -55,7 +55,7 @@ def label_names(text):
         tail = text[m.end(): m.end() + 200]
         close = tail.find("}\n")
         chunk = tail[: close if close != -1 else None].split("\n", 1)[0]
-        for key in re.findall(r"([a-zA-Z_][a-zA-Z0-9_]*)\s*=\s*[\"'{]", chunk):
+        for key in re.findall(r"([a-zA-Z_][a-zA-Z0-9_]*)\s*=\s*\\?[\"'{]", chunk):
             found.add(key)
     return found