ci: skip a prerelease tag in all four publishers

Their trigger is `v*`, which matches `v0.4.0-beta.1`. They guarded
`v0.0.0` -- the version floor -- and nothing else, so the first
prerelease tag would have published a beta everywhere.

Nothing produces one today. The guard is here because the thing that
would is `prerelease: true` in .releaserc.yml, a one-line change whose
blast radius is four public channels and which nothing in those four
files mentions. That is the same argument release.yml's `chore(release):`
guard is kept on: cheap, against something a future edit turns on
somewhere else entirely.

android-apk is the worst of the four twice over. Its APK goes to the
*generic* registry, which is readable without credentials so Obtainium
can poll a plain URL, so a beta would be offered to every device on it.
And its versionCode maths splits on dots: it would read "1" out of
"0-beta" and produce a wrong number rather than a failed build, which
matters because Android orders releases by that integer and refuses
anything not greater than what is installed.

Each is a clean skip rather than a failure, matching the v0.0.0 guard
beside it: a red run against a tag that was never meant to ship is noise.

.gitea/workflows/homebrew-formula.yml

@@ -56,6 +56,18 @@ jobs:
             echo "skip=true" >> "$GITHUB_OUTPUT"
             exit 0
           fi
+
+          # Nor is a prerelease, and this trigger is `v*`, which matches
+          # `v0.4.0-beta.1`.  It matters most here of the four: the tap
+          # is public, and `brew upgrade` would offer a beta to everyone
+          # on it.
+          case "$VERSION" in
+            *-*)
+              echo "$TAG is a prerelease; not syncing it to a public tap"
+              echo "skip=true" >> "$GITHUB_OUTPUT"
+              exit 0
+              ;;
+          esac
           echo "skip=false" >> "$GITHUB_OUTPUT"
 
           TARBALL="${SOURCE_TARBALL_BASE}/${TAG}.tar.gz"