build(ci): don't store screenshots on most PRs

Store only needs to be executed on `main`

We run on some file changes, in case they break the upload process, but
this is only defensive.

Note: this does upload artifacts, this could be avoided, but the
complexity makes the 'happy path' of this workflow harder to reason
about.

Issue 20942

Assisted-by: Claude Opus 4.7

Author: david-allison

.github/workflows/screenshot_store.yml

@@ -26,7 +26,15 @@ on:
   push:
     branches:
       - main
+  # On PRs, only run this when structural changes occur, to be sure 'main' can still store baselines
   pull_request:
+    paths:
+      - '.github/workflows/screenshot_*.yml'
+      - 'gradle/libs.versions.toml'
+      - 'AnkiDroid/build.gradle'
+      - 'AnkiDroid/build.gradle.kts' # future-proof
+      - '**/ScreenshotTest.kt'
+      - 'tools/compare-screenshot-test.sh'
 
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