Add Clang 16 to the build matrix.

... and remove Clang 13 so that we continue to
test with only the three most recent releases.

Change-Id: I0ee7e7f252e364d641430ba6c99270d858f70e73
Reviewed-on: https://code-review.googlesource.com/c/re2/+/61190
Reviewed-by: Perry Lorier <perryl@google.com>
Reviewed-by: Paul Wankadia <junyer@google.com>
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 807a5ca..8b01d57 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -27,7 +27,7 @@
     strategy:
       fail-fast: false
       matrix:
-        ver: [13, 14, 15]
+        ver: [14, 15, 16]
     env:
       CC: clang-${{ matrix.ver }}
       CXX: clang++-${{ matrix.ver }}