Replace PGP signing action with the bash script from the same

The PGP signing action ultimately just calls gpg with arguments
set in
https://github.com/actionhippie/gpgsign/blob/v1/overlay/usr/local/bin/entrypoint
so its rather trivial to simply take the required arguments and
put them directly in CI.

This is substantially safer than the PGP signing action used as the
action currently downloads, unverified and un-pinned, a docker
image in order to access PGP.

.github/workflows/prod-deploy.yml

@@ -21,12 +21,15 @@ jobs:
       - name: Create tar.gz
         run: tar -czvf cinny-${{ steps.vars.outputs.tag }}.tar.gz dist
       - name: Sign tar.gz
-        uses: actionhippie/gpgsign@4e28208b142cae93e1582401dcda1cf79e4f72c0
-        with:
-          private_key: ${{ secrets.GNUPG_KEY }}
-          passphrase: ${{ secrets.GNUPG_PASSPHRASE }}
-          detach_sign: true
-          files: cinny-${{ steps.vars.outputs.tag }}.tar.gz
+        run: |
+          echo '${{ secrets.GNUPG_KEY }}' | gpg --batch --import
+          # Sadly a few lines in the private key match a few lines in the public key,
+          # As a result just --export --armor gives us a few lines replaced with ***
+          # making it useless for importing the signing key. Instead, we dump it as
+          # non-armored and hex-encode it so that its printable.
+          echo "PGP Signing key, in raw PGP format in hex. Import with cat ... | xxd -r -p - | gpg --import"
+          gpg --export | xxd -p
+          echo '${{ secrets.GNUPG_PASSPHRASE }}' | gpg --batch --yes --pinentry-mode loopback --passphrase-fd 0 --armor --detach-sign cinny-${{ steps.vars.outputs.tag }}.tar.gz
       - name: Upload tagged release
         uses: softprops/action-gh-release@1e07f4398721186383de40550babbdf2b84acfc5
         with: