Prepare to tag release `2024-04-01`.

Change-Id: Ib26837e1d2d63ce13b1ef171c5c1af8168b94448
Reviewed-on: https://code-review.googlesource.com/c/re2/+/62910
Reviewed-by: Jeff Bailey <jeffbailey@google.com>
Reviewed-by: Paul Wankadia <junyer@google.com>