CI: rename env vars for Central credentials

I am not certain whether existing user tokens were migrated over,
but my initial test did not look promising. In the interest of clarity,
this change renames the variable prefix from OSSRH_ to CENTRAL_.

On the scijava-scripts side, the ci-build.sh script can look for the
correct environment variables, and fail fast with a nice message when
the old variables are still set.

Author: ctrueden

.github/workflows/build.yml

@@ -31,5 +31,6 @@ jobs:
           GPG_PASSPHRASE: ${{ secrets.GPG_PASSPHRASE }}
           MAVEN_USER: ${{ secrets.MAVEN_USER }}
           MAVEN_PASS: ${{ secrets.MAVEN_PASS }}
-          OSSRH_PASS: ${{ secrets.OSSRH_PASS }}
+          CENTRAL_USER: ${{ secrets.CENTRAL_USER }}
+          CENTRAL_PASS: ${{ secrets.CENTRAL_PASS }}
           SIGNING_ASC: ${{ secrets.SIGNING_ASC }}