Add GCC 12 to the build matrix.

Change-Id: Ibb389e3044c1932b908bc330a36a85dd7ad73ca8
Reviewed-on: https://code-review.googlesource.com/c/re2/+/60110
Reviewed-by: Perry Lorier <perryl@google.com>
Reviewed-by: Paul Wankadia <junyer@google.com>
1 file changed