Fix trying to push mastodon-streaming docker images to upstream's ghcr repo (#2541)

.github/workflows/build-nightly.yml

@@ -51,7 +51,7 @@ jobs:
       use_native_arm64_builder: false
       cache: false
       push_to_images: |
-        ghcr.io/mastodon/mastodon-streaming
+        ghcr.io/${{ github.repository_owner }}/mastodon-streaming
       version_prerelease: ${{ needs.compute-suffix.outputs.prerelease }}
       labels: |
         org.opencontainers.image.description=Nightly build image used for testing purposes

.github/workflows/build-push-pr.yml

@@ -49,7 +49,7 @@ jobs:
       platforms: linux/amd64,linux/arm64
       use_native_arm64_builder: false
       push_to_images: |
-        ghcr.io/mastodon/mastodon-streaming
+        ghcr.io/${{ github.repository_owner }}/mastodon-streaming
       version_metadata: ${{ needs.compute-suffix.outputs.metadata }}
       flavor: |
         latest=auto

.github/workflows/build-releases.yml

@@ -36,7 +36,7 @@ jobs:
       platforms: linux/amd64,linux/arm64
       use_native_arm64_builder: false
       push_to_images: |
-        ghcr.io/mastodon/mastodon-streaming
+        ghcr.io/${{ github.repository_owner }}/mastodon-streaming
       # Do not use cache when building releases, so apt update is always ran and the release always contain the latest packages
       cache: false
       # Only tag with latest when ran against the latest stable branch