ci: adopt recent branch rename

Lukas Puehringer · Lukas Puehringer · commit 717f73ae6667 · 2023-03-07T15:29:56.000+01:00
Signed-off-by: Lukas Puehringer &lt;lukas.puehringer@nyu.edu&gt;
diff --git a/.github/workflows/test-sigstore.yml b/.github/workflows/test-sigstore.yml
@@ -3,7 +3,7 @@ name: Run Sigstore Signer tests
 on:
   push:
     branches:
-      - master
+      - main
   pull_request:
   workflow_dispatch:
 
