Update link to community repo

The default branch is `main`, not `master`. Following the existing link shows you a redirect warning in the GitHub UI

Closes #19157.

PiperOrigin-RevId: 553544682
Change-Id: Ic9304f43462d2549f57ee132df623743acc9fa22

site/en/community/sig.md

@@ -23,7 +23,7 @@ established. Before joining, review the group's work, and then get in touch
 with the SIG leader. Membership policies vary on a per-SIG basis.
 
 See the complete list of
-[Bazel SIGs](https://github.com/bazelbuild/community/tree/master/sigs){: .external}.
+[Bazel SIGs](https://github.com/bazelbuild/community/tree/main/sigs){: .external}.
 
 ### Non-goals: What a SIG is not