set versionCode for nightly builds only in gitlab-ci

Having dynamic build config variables breaks instant APK updates:
https://developer.android.com/studio/build/optimize-your-build#use_static_build_properties

.gitlab-ci.yml

@@ -96,6 +96,9 @@ deploy_nightly:
     - echo "<item>${CI_PROJECT_PATH}-nightly</item>" >> app/src/main/res/values/default_repos.xml
     - echo "<item>${CI_PROJECT_URL}-nightly/raw/master/fdroid/repo</item>" >> app/src/main/res/values/default_repos.xml
     - cat config/nightly-repo/repo.xml >> app/src/main/res/values/default_repos.xml
+    - export DB=`sed -n 's,.*DB_VERSION *= *\([0-9][0-9]*\).*,\1,p' app/src/main/java/org/fdroid/fdroid/data/DBHelper.java`
+    - export versionCode=`printf '%d%05d' $DB $(date '+%s'| cut -b4-8)`
+    - sed -i "s,^\(\s*versionCode\)  *[0-9].*,\1 $versionCode," app/build.gradle
     # build the APKs!
     - ./gradlew assembleDebug
     - fdroid nightly -v

app/build.gradle

@@ -59,32 +59,7 @@ android {
             applicationIdSuffix ".debug"
             resValue "string", "applicationId", defaultConfig.applicationId + applicationIdSuffix
             versionNameSuffix "-debug"
-        }
-    }
-
-    /* set the debug versionCode based on DB verson and how many commits in the repo */
-    applicationVariants.all { variant ->
-        if (variant.buildType.isDebuggable()) {
-            // default to a timestamp, in case anything fails later
-            variant.mergedFlavor.versionCode = new Date().getTime() / 1000
-            try {
-                def stdout = new ByteArrayOutputStream()
-                exec {
-                    commandLine 'git', 'rev-list', '--first-parent', '--count', 'HEAD'
-                    standardOutput = stdout
-                }
-                def commitCount = Integer.parseInt(stdout.toString().trim())
-                stdout = new ByteArrayOutputStream()
-                exec {
-                    commandLine 'sed', '-n', 's,.*DB_VERSION *= *\\([0-9][0-9]*\\).*,\\1,p', 'src/main/java/org/fdroid/fdroid/data/DBHelper.java'
-                    standardOutput = stdout
-                }
-                def dbVersion = Integer.parseInt(stdout.toString().trim())
-                println 'Setting debug versionCode: ' + sprintf("%d%05d", [dbVersion, commitCount])
-                variant.mergedFlavor.versionCode = Integer.parseInt(sprintf("%d%05d", [dbVersion, commitCount]))
-            }
-            catch (ignored) {
-            }
+            println 'buildTypes.debug defaultConfig.versionCode ' + defaultConfig.versionCode
         }
     }