Fix GPR auth: use credentials file instead of env var (#14)

Author: djbender

.github/workflows/release.yml

@@ -25,10 +25,14 @@ jobs:
     - name: Build gem
       run: gem build lizard.gemspec
 
+    - name: Set up GPR credentials
+      run: |
+        mkdir -p ~/.gem
+        echo -e "---\n:github: Bearer ${{ secrets.GITHUB_TOKEN }}" > ~/.gem/credentials
+        chmod 0600 ~/.gem/credentials
+
     - name: Publish to GitHub Packages
-      env:
-        GEM_HOST_API_KEY: Bearer ${{ secrets.GITHUB_TOKEN }}
-      run: gem push --host https://rubygems.pkg.github.com/djbender lizard-*.gem
+      run: gem push --key github --host https://rubygems.pkg.github.com/djbender lizard-*.gem
 
     - name: Create GitHub Release
       env: