Use consistent braces for the lldb-python substitution

Author: tbkka

test/lit.cfg

@@ -1967,7 +1967,7 @@ if config.lldb_build_root != "":
         else:
             config.available_features.add('lldb')
             config.substitutions.append(('%lldb-python-path', lldb_python_path))
-            config.substitutions.append(('%lldb-python', 'PYTHONPATH=%s %s' % (lldb_python_path, lldb_python)))
+            config.substitutions.append(('%{lldb-python}', 'PYTHONPATH=%s %s' % (lldb_python_path, lldb_python)))
 
 # Disable randomized hash seeding by default. Tests need to manually opt in to
 # random seeds by unsetting the SWIFT_DETERMINISTIC_HASHING environment