ci: fix Maven GPG import input name (#182)

crazy-max/ghaction-import-gpg@v7 expects 'gpg_private_key' (underscore);
the workflow used 'gpg-private-key' (hyphen), which was silently ignored
and caused 'Input required and not supplied: gpg_private_key', failing the
Maven Central release for 1.5.0-RC2.

Author: jadamcrain

.github/workflows/ci.yml

@@ -362,7 +362,7 @@ jobs:
       - name: Import PGP key
         uses: crazy-max/ghaction-import-gpg@v7
         with:
-          gpg-private-key: ${{ secrets.SFIO_PGP_PRIVATE_KEY }}
+          gpg_private_key: ${{ secrets.SFIO_PGP_PRIVATE_KEY }}
           passphrase: ${{ secrets.SFIO_PGP_PRIVATE_KEY_PASSPHRASE }}
       - name: Deploy Java to Maven Central
         shell: bash