Fix downstream python format to match upstream

Fix python lint violation. NFC.

Author: cachemeifyoucan

llvm/test/lit.cfg.py

@@ -800,7 +800,7 @@ def host_unwind_supports_jit():
     config.available_features.add("expensive_checks")
 
 if config.have_ondisk_cas:
-    config.available_features.add('ondisk_cas')
+    config.available_features.add("ondisk_cas")
 
 if "MemoryWithOrigins" in config.llvm_use_sanitizer:
     config.available_features.add("use_msan_with_origins")