Fix test_files-clang failure with Clang 16

The test built against Clang 16.0.0 fails with the following output:
QDEBUG : TestFiles::testFiles(templates.cpp) "type" FAILED: Declaration's type did not pass tests. (Declaration on line 59 in /builds/devv/kdevelop/plugins/clang/tests/files/templates.cpp)
QDEBUG : TestFiles::testFiles(templates.cpp)  "toString" FAILED: Type's toString ("SpacedDefaultParam<  >") doesn't match test data ("SpacedDefaultParam< 20 >").
...
FAIL!  : TestFiles::testFiles(templates.cpp) 'validator.testsPassed()' returned FALSE. ()
   Loc: [/builds/devv/kdevelop/plugins/clang/tests/test_files.cpp(195)]