k9: fix gradle version detection

gradle.properties

@@ -0,0 +1,2 @@
+org.gradle.jvmargs=-Xmx1g
+org.gradle.jvmargs=-Xmx1g

metadata/com.fsck.k9.yml

@@ -477,13 +477,17 @@ Builds:
   - versionName: '5.701'
     versionCode: 27001
     commit: '5.701'
-    subdir: app/k9mail
     gradle:
       - yes
+    output: app/k9mail/build/outputs/apk/release/k9mail-release-unsigned.apk
     rm:
       - tools/android-studio/settings.jar
     prebuild: echo 'org.gradle.jvmargs=-Xmx1g' >> ../../gradle.properties
 
+MaintainerNotes: |-
+    Use output instead of subdir to make gradlew-fdroid correctly determine the gradle version to be used.
+    It doesn't work when using subdir because we are two levels deep into thedirectory structure.
+
 AutoUpdateMode: Version %v
 UpdateCheckMode: RepoManifest/5.6-MAINT
 CurrentVersion: '5.600'