release-plz: don't set CARGO_REGISTRY_TOKEN, not even to an empty string

Author: Firestar99

.github/workflows/release-plz.yml

@@ -34,7 +34,6 @@ jobs:
           command: release
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-          CARGO_REGISTRY_TOKEN: ${{ secrets.CARGO_REGISTRY_TOKEN }}
 
   # Create a PR with the new versions and changelog, preparing the next release.
   release-plz-pr:
@@ -56,4 +55,3 @@ jobs:
           command: release-pr
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-          CARGO_REGISTRY_TOKEN: ${{ secrets.CARGO_REGISTRY_TOKEN }}