Add Clang 15 to the build matrix.

Change-Id: I34d611dd8f506d478813b431c411b311308d7bfc
Reviewed-on: https://code-review.googlesource.com/c/re2/+/60452
Reviewed-by: Andy Miller <armil@google.com>
Reviewed-by: Paul Wankadia <junyer@google.com>
1 file changed