Change Ubuntu builder to Ubuntu version supported until 2028

Author: kiwibrowser

.github/workflows/build_apk.yml

@@ -9,7 +9,7 @@ on:
 jobs:
   build:
     # The type of runner that the job will run on
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-18.04
 
     strategy:
       fail-fast: false