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/android.yml

@@ -17,10 +17,12 @@ on:
     paths:
       - 'android/**'
       - '.gitea/workflows/android.yml'
-  pull_request:
-    branches: [main]
-    paths:
-      - 'android/**'
+
+# pull_request trigger intentionally omitted — see test-web.yml for
+# the rationale (single-author repo, push covers PR-merge equivalent).
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
 
 env:
   # Silences the JDK 22+ "restricted method in java.lang.System has been