docs: fix env var in release instructions

README.md

@@ -258,7 +258,7 @@ git tag -a v<semver> -m "Release summary"
 git push origin v<semver>
 # login to ghcr too
 # https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-container-registry#authenticating-with-a-personal-access-token-classic
-echo $CR_PAT | docker login ghcr.io -u $USERNAME --password-stdin
+echo $GITHUB_TOKEN | docker login ghcr.io -u $USERNAME --password-stdin
 
 goreleaser release
 ```