CI: a branch's pushes run nothing, its pull request runs once

A branch with an open pull request ran twice per push: once for the push,
once for the pull request. Pushes to main still run the tests and publish
the badges; every other branch is tested by its pull request.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

.gitea/workflows/ci.yml

@@ -1,7 +1,8 @@
 # CI and releases (docs/milestones/R1.md).
-#   A push:            the host tests, with their coverage of lib/. On main, the README's badges
-#                      are published to the branch `badges`.
-#   A pull request:    the same, then the release firmware and the Debug Build.
+#   A push to main:    the host tests, with their coverage of lib/, and the README's badges
+#                      published to the branch `badges`.
+#   A pull request:    the same tests and coverage, then the release firmware and the Debug Build.
+#                      A branch's pushes run nothing by themselves: its pull request runs, once.
 #   A tag v*:          all of it, then a Gitea release with the signed Update File.
 #   Run by hand:       the release of a tag that exists already (the ones from before CI).
 #
@@ -11,7 +12,7 @@
 name: CI
 on:
   push:
-    branches: ['**', '!badges']  # badges holds what CI itself publishes
+    branches: [main]  # other branches are tested by their pull request: one run, not two
     tags: ['v*']
   pull_request:
   workflow_dispatch: