Merge pull request #53 from cryptomator/ci-hardening

Hardening the CI in relation to PRs

Author: SailReal

.github/workflows/build.yml

@@ -1,6 +1,8 @@
 name: Build
 on:
-  [push]
+  push:
+  pull_request_target:
+    types: [labeled]
 jobs:
   build:
     name: Build and Test
@@ -68,4 +70,4 @@ jobs:
             ```
 
             See [README.md](https://github.com/cryptomator/siv-mode/#reproducible-builds) section regarding reproducing this build.
-          generate_release_notes: true
+          generate_release_notes: true