Revert AGP to 8.11.1 to unblock F-Droid build.

Reason: #3420 (comment)

Author: bmarty

gradle/libs.versions.toml

@@ -3,7 +3,8 @@
 
 [versions]
 # Project
-android_gradle_plugin = "8.12.2"
+# We cannot use 8.12.+ since it breaks F-Droid build (see https://github.com/element-hq/element-x-android/issues/3420#issuecomment-3199571010)
+android_gradle_plugin = "8.11.1"
 # When updateing this, please also update the version in the file ./idea/kotlinc.xml
 kotlin = "2.2.10"
 kotlinpoet = "2.2.0"