ci: fix cancel for main

.github/workflows/rust.yml

@@ -8,8 +8,8 @@ on:
 
 concurrency:
   # Documentation suggests ${{ github.head_ref }}, but that's only available on pull_request/pull_request_target triggers, so using ${{ github.ref }}.
-  # On master, we want all builds to complete even if merging happens faster to make it easier to discover at which point something broke.
-  group: ${{ github.ref == 'refs/heads/master' && format('ci-master-{0}', github.sha) || format('ci-{0}', github.ref) }}
+  # On main, we want all builds to complete even if merging happens faster to make it easier to discover at which point something broke.
+  group: ${{ github.ref == 'refs/heads/main' && format('ci-main-{0}', github.sha) || format('ci-{0}', github.ref) }}
   cancel-in-progress: true
 
 env: