Update GHA conditions

Author: bbayles

.github/workflows/build_test.yml

@@ -1,6 +1,17 @@
 name: Build and test
 
-on: [push, pull_request]
+on:
+  pull_request:
+    types: [opened, synchronize, reopened, ready_for_review]
+    paths-ignore:
+      - '**.rst'
+      - 'docs/**'
+  push:
+    branches:
+      - main
+    paths-ignore:
+      - '**.rst'
+      - 'docs/**'
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}