ci: Ignore l10n_master from Crowdin

Crowding commits each language in its own commit, instead of merging multiple into one commit. This results in very spammy builds, to the point of several hundred being spawned in the same second.

.github/workflows/main.yml

@@ -1,6 +1,12 @@
 name: Build
 
-on: [push, pull_request]
+on:
+  push:
+    branches-ignore:
+      - 'l10n_master'
+  pull_request:
+    branches-ignore:
+      - 'l10n_master'
 
 jobs:
   windows: