ci: don't run workflows twice in PRs (#35)

Closes #34

Author: StyleShit

.github/workflows/ci.yml

@@ -1,6 +1,11 @@
 name: CI
 
-on: [push, pull_request]
+on:
+    push:
+        branches:
+            - main
+
+    pull_request:
 
 concurrency:
     group: ${{ github.workflow }}-${{ github.ref }}