Accept only 'true' for a true value to align with other code.

Author: michaelsafyan

instrumentation-genai/opentelemetry-instrumentation-google-genai/src/opentelemetry/instrumentation/google_genai/flags.py

@@ -21,4 +21,4 @@ def is_content_recording_enabled():
     return os.getenv(
         _CONTENT_RECORDING_ENV_VAR,
         "false"
-    ).lower() in ["1", "true", "yes", "on"]
+    ).lower() == "true"