fix(ci): write GPG key directly to file instead of importing and exporting

No need to import the key into GPG and then export it again. Just
write the secret key data directly to a file for nfpm to use.

.github/workflows/release.yml

@@ -176,16 +176,9 @@ jobs:
         uses: actions/download-artifact@37930b1c2abaa49bbe596cd826c3c89aef350131 # v7
         with:
           name: mage_bin
-      - name: GPG setup
+      - name: Write GPG key for nfpm
         if: matrix.package == 'rpm'
-        uses: kolaente/action-gpg@main
-        with:
-          gpg-passphrase: "${{ secrets.RELEASE_GPG_PASSPHRASE }}"
-          gpg-sign-key: "${{ secrets.RELEASE_GPG_SIGN_KEY }}"
-      - name: Export GPG key for nfpm
-        if: matrix.package == 'rpm'
-        run: |
-          gpg --export-secret-keys --armor 7D061A4AA61436B40713D42EFF054DACD908493A > /tmp/nfpm-signing-key.gpg
+        run: echo -n "${{ secrets.RELEASE_GPG_SIGN_KEY }}" > /tmp/nfpm-signing-key.gpg
       - name: Prepare
         env:
           RELEASE_VERSION: ${{ steps.ghd.outputs.describe }}