Fix 3pl guard exclusion

Author: allison-grady

.github/workflows/3pl-guard.yml

@@ -124,10 +124,13 @@ jobs:
             });
 
             // Ignore package.json under test fixtures (e.g. e2e workspace-detection fixtures)
-            const fixtureManifestPattern = /[/\\]test[/\\].*[/\\]fixtures[/\\].*package\.json$/i;
+            const isTestFixtureManifest = (filename) =>
+              filename.endsWith('package.json') &&
+              filename.includes('/test/') &&
+              filename.includes('/fixtures/');
             const changedPackageJsonFiles = files
               .map((file) => file.filename)
-              .filter((filename) => filename.endsWith('package.json') && !fixtureManifestPattern.test(filename));
+              .filter((filename) => filename.endsWith('package.json') && !isTestFixtureManifest(filename));
 
             const findings = [];