ci: drop the temporary feat/postgres triggers

The extra branch filters existed so the stacked PostgreSQL PRs (which
targeted feat/postgres instead of main) got the full pipeline. All of
those PRs have merged, and this umbrella PR is covered by the original
main filter, so the addition now only produces duplicate runs (the
push-triggered run plus this PR's synchronize run on every merge).

Author: dcoric

.github/workflows/ci.yml

@@ -5,9 +5,9 @@ name: CI
 
 on:
   push:
-    branches: [main, feat/postgres]
+    branches: [main]
   pull_request:
-    branches: [main, feat/postgres]
+    branches: [main]
 
 permissions:
   pull-requests: write