Revert "Tag latest main commit as "main" in DockerHub"

This reverts commit 09a747b.

Well, I can't get it to work. Never mind. Should probably just write a
shell script instead of all these obscure GitHub actions with bizarre
unreadable overcomplex TypeScript stuff.

Author: arp242

.github/workflows/build.yml

@@ -30,11 +30,7 @@ jobs:
         id: 'meta'
         with:
           images: 'arp242/goatcounter'
-          tags: |
-            type=semver,pattern={{version}}
-            type=semver,pattern={{major}}.{{minor}}
-            type=sha
-            type=ref,event=push,branch=main
+          tags:   "type=semver,pattern={{version}}\ntype=semver,pattern={{major}}.{{minor}}\ntype=sha"
       - uses: 'docker/build-push-action@v6'
         with:
           context:    '.'