fix(ci): use upstream default branch master for prerelease polling

The mistral.rs repo uses master as its default branch, not main.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/poll-upstream.yml

@@ -92,7 +92,7 @@ jobs:
         run: |
           response=$(curl --silent --show-error --fail --location \
             --header 'Accept: application/vnd.github+json' \
-            --url 'https://api.github.com/repos/EricLBuehler/mistral.rs/commits/main')
+            --url 'https://api.github.com/repos/EricLBuehler/mistral.rs/commits/master')
           sha=$(echo "${response}" | jq -r .sha)
           short_sha=$(echo "${sha}" | head --bytes=7)
           date=$(echo "${response}" | jq -r '.commit.committer.date[:10]' | tr -d '-')