sagemathgh-36466: Run incremental linux ci only when packages changed

    
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... so that it only shows up in the "checks" list below in these cases.

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URL: sagemath#36466
Reported by: Tobias Diez
Reviewer(s): Kwankyu Lee, Matthias Köppe, Tobias Diez

.github/workflows/ci-linux-incremental.yml

@@ -24,6 +24,9 @@ on:
       - reopened
       # When a CI label is added
       - labeled
+    paths:
+      - 'build/pkgs/**'
+      - 'pkgs/**'
   workflow_dispatch:
 
 concurrency: