Disable `@_implementationOnly` check for `FirebaseVertexAI`

scripts/check_imports.swift

@@ -84,7 +84,11 @@ private func checkFile(_ file: String, logger: ErrorLogger, inRepo repoURL: URL,
     // Swift specific checks.
     fileContents.components(separatedBy: .newlines)
       .enumerated() // [(lineNum, line), ...]
-      .filter { $1.starts(with: "import FirebaseCoreExtension") }
+      .filter {
+        $1.starts(with: "import FirebaseCoreExtension")
+          /* FirebaseVertexAI is using `InternalImportsByDefault` so its files are not checked. */
+          && !file.contains("FirebaseVertexAI")
+      }
       .forEach { lineNum, line in
         logger
           .importLog(