Use var instead of secrets for OSSRH_USERNAME

Author: hiroyuki-sato

Diff for: .github/workflows/publish.yml

@@ -25,7 +25,7 @@ jobs:
         printf -- "---\n:rubygems_api_key: ${RUBYGEMS_API_KEY}\n" > $HOME/.gem/credentials
         ./gradlew --stacktrace publishMavenPublicationToMavenCentralRepository gemPush
       env:
-        ORG_GRADLE_PROJECT_ossrhUsername: ${{ secrets.OSSRH_USERNAME }}
+        ORG_GRADLE_PROJECT_ossrhUsername: ${{ vars.OSSRH_USERNAME }}
         ORG_GRADLE_PROJECT_ossrhPassword: ${{ secrets.OSSRH_PASSWORD }}
         ORG_GRADLE_PROJECT_signingKey: ${{ secrets.GPG_PRIVATE_KEY_ARMOR }}
         ORG_GRADLE_PROJECT_signingPassword: ${{ secrets.GPG_PRIVATE_KEY_PASSWORD }}