Bug 261309

check-webkit-style assertion failure in Source/WebCore/PAL/ThirdParty/libavif/ThirdParty/dav1d/src/thread_task.c.

Note that I've added some debugging output below as well:

```
$ ./Tools/Scripts/check-webkit-style --filter="-,+runtime/wtf_make_unique" Source/WebCore/PAL/ThirdParty/libavif/ThirdParty/dav1d/src/thread_task.c
[...]
>>> check_identifier_name_in_declaration(Source/WebCore/PAL/ThirdParty/libavif/ThirdParty/dav1d/src/thread_task.c, 422,     case DAV1D_TASK_TYPE_FG_APPLY:;, ...)
>>> _check_identifier_name_for_acronyms(DAV1D_TASK_TYPE_FG_APPLY:)
>>> _split_identifier_into_words(DAV1D_TASK_TYPE_FG_APPLY:)
Traceback (most recent call last):
  File "./Tools/Scripts/check-webkit-style", line 46, in <module>
    sys.exit(CheckWebKitStyle().main())
  File "Tools/Scripts/webkitpy/style/main.py", line 153, in main
    file_reader.process_paths(paths)
  File "Tools/Scripts/webkitpy/style/filereader.py", line 149, in process_paths
    self.process_file(path)
  File "Tools/Scripts/webkitpy/style/filereader.py", line 137, in process_file
    self._processor.process(lines, file_path, **kwargs)
  File "Tools/Scripts/webkitpy/style/checker.py", line 1103, in process
    checker.check(lines)
  File "Tools/Scripts/webkitpy/style/checkers/cpp.py", line 4811, in check
    _process_lines(self.file_path, self.file_extension, lines,
  File "Tools/Scripts/webkitpy/style/checkers/cpp.py", line 4643, in _process_lines
    process_line(filename, file_extension, clean_lines, line,
  File "Tools/Scripts/webkitpy/style/checkers/cpp.py", line 4588, in process_line
    check_language(filename, clean_lines, line, file_extension, include_state,
  File "Tools/Scripts/webkitpy/style/checkers/cpp.py", line 4044, in check_language
    check_identifier_name_in_declaration(filename, line_number, line, file_state, error)
  File "Tools/Scripts/webkitpy/style/checkers/cpp.py", line 4215, in check_identifier_name_in_declaration
    _check_identifier_name_for_acronyms(identifier, line_number, is_class_or_namespace_or_struct_name, error)
  File "Tools/Scripts/webkitpy/style/checkers/cpp.py", line 1918, in _check_identifier_name_for_acronyms
    identifier_words = _split_identifier_into_words(identifier)
  File "Tools/Scripts/webkitpy/style/checkers/cpp.py", line 1903, in _split_identifier_into_words
    assert False, 'Could not match "%s"' % identifier
AssertionError: Could not match ":"
```