CI: fix duplicate test runs on pull requests (#13)

Limit push trigger to main branch only. This prevents tests from running
twice (once for push, once for pull_request) when pushing to PR branches.

Author: messa

.github/workflows/test-device.yml

@@ -1,6 +1,9 @@
 name: Test on block devices
 
-on: [push, pull_request]
+on:
+  push:
+    branches: [main]
+  pull_request:
 
 permissions:
   contents: read

.github/workflows/test-with-uv.yml

@@ -1,6 +1,9 @@
 name: Test with uv
 
-on: [push, pull_request]
+on:
+  push:
+    branches: [main]
+  pull_request:
 
 permissions:
   contents: read

.github/workflows/test.yml

@@ -1,6 +1,9 @@
 name: Test
 
-on: [push, pull_request]
+on:
+  push:
+    branches: [main]
+  pull_request:
 
 permissions:
   contents: read