ci: drop pull_request triggers + add cancel-in-progress concurrency

Every commit on dev that's part of an open PR fires each workflow
TWICE: once for the push event and once for the pull_request event
(observable in run #43 + #44 for the same SHA in android.yml, same
shape across test-web.yml and test-go.yml). The two runs check the
exact same SHA — pure waste.

Drop the pull_request trigger from test-web.yml, test-go.yml, and
android.yml. The dev push already exercises every check that a PR
would re-run. This repo has no fork PRs to cover, which is the only
case pull_request would catch that push doesn't.

Add a concurrency group keyed on workflow + ref with
cancel-in-progress: true to every workflow including release.yml.
Rapid re-pushes (or force-moving the per-day tag) now cancel the
older in-flight run instead of stacking.

.gitea/workflows/release.yml

@@ -26,6 +26,13 @@ on:
       - '**/*.md'
   workflow_dispatch:
 
+# Force-moving the per-day tag (or rapidly re-pushing to main) should
+# supersede the in-flight build — the operator explicitly wants the
+# later commit to win.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   release:
     runs-on: go-ci