Fix release job: give gh the repo via GH_REPO

The release job has no repo checkout, so `gh release create` failed with
"fatal: not a git repository" when resolving the target repo. Setting
GH_REPO from github.repository lets gh target the repo without a checkout.

The v8.0.0 builds succeeded but this step failed; the draft release was
created manually as a workaround. This makes future tag releases automatic.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01R1UgwVVGtcUmjzSL5yoK4w

Author: eliasdoehne

.github/workflows/build.yml

@@ -88,6 +88,9 @@ jobs:
       - name: Create Release Draft
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          # gh needs to know the target repo; the release job has no checkout,
+          # so without this gh fails with "fatal: not a git repository".
+          GH_REPO: ${{ github.repository }}
         run: |
           gh release create ${{ github.ref_name }} release_files/* --draft --generate-notes