Prevent Sphinx error when category is empty

docs/tools/test_spec_gen.py

@@ -78,6 +78,8 @@ def _write_suite(file: TextIO, metadata: Dict[str, str]) -> None:
 
     file.write("    :platform: ``Azure, Ready``\n")  # Platform
     file.write(f"    :area: ``{metadata['area']}``\n")  # Area
+
+    if metadata["category"]:
         file.write(f"    :category: ``{metadata['category']}``\n\n")  # Category