Add build-args for RELEASE_VERSION in Docker workflow

Author: TylerS1066

.github/workflows/docker.yaml

@@ -28,6 +28,8 @@ jobs:
           context: .
           file: ./Dockerfile
           push: true
+          build-args: |
+            RELEASE_VERSION=${{ github.event.release.tag_name }}
           tags: |
             ghcr.io/apdevteam/modmail:${{ github.event.release.tag_name }}
-            ghcr.io/apdevteam/modmail:latest
+            ghcr.io/apdevteam/modmail:latest