Fix version stripping in GitHub action to prevent double 'v' prefix

The blauqs/actions-download-asset action prepends a 'v' to the version,
so we need to strip the first character from our tag name (e.g., 'vjamscribe-2'
becomes 'jamscribe-2') to avoid 'vvjamscribe-2' format.

Co-authored-by: Michael Kochell <mickmister@users.noreply.github.com>

Author: claude[bot]

.github/actions/build-rpi-image/action.yml

@@ -51,7 +51,7 @@ runs:
               map(select(.tagName | startswith($prefix)))
               | sort_by(.publishedAt)
               | last
-              | if . == null then "none" else .tagName end
+              | if . == null then "none" else .tagName[1:] end
             ')
         echo "latest_tag=$latest" >> $GITHUB_OUTPUT
         echo "Found latest release: $latest"