Set stop_on_error (#24453)

Current air version runs the old binary if the build fails. This
restores the old behaviour.

```
...
code.gitea.io/gitea/services/cron
code.gitea.io/gitea/routers/web/user/setting
code.gitea.io/gitea/routers/web/org
make[2]: *** [Makefile:814: gitea] Error 1
make[2]: Leaving directory '/src'
failed to build, error: exit status 2
running...
2023/04/30 21:04:11 cmd/web.go:125:runWeb() [I] Starting Gitea on PID: 29153
2023/04/30 21:04:11 cmd/web.go:178:runWeb() [I] Global init
...
```

Reference: https://github.com/cosmtrek/air/pull/336

.air.toml

@@ -10,3 +10,4 @@ include_file = ["main.go"]
 include_dir = ["cmd", "models", "modules", "options", "routers", "services"]
 exclude_dir = ["modules/git/tests", "services/gitdiff/testdata", "modules/avatar/testdata", "models/fixtures", "models/migrations/fixtures", "modules/migration/file_format_testdata", "modules/avatar/identicon/testdata"]
 exclude_regex = ["_test.go$", "_gen.go$"]
+stop_on_error = true