Upgrade Gradle and Plugin to 8 and fix warnings

build.gradle

@@ -17,7 +17,7 @@
  * along with the Cyface Publish Plugin for Android. If not, see <http://www.gnu.org/licenses/>.
  */
 buildscript {
-    ext.gradle_version = '7.4.2' // Major release available but breaks publish [RFR-412]
+    ext.gradle_version = '8.2.2'
 
     repositories {
         google()

gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,6 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-7.6.1-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.6-all.zip
 networkTimeout=10000
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists

src/main/groovy/de.cyface.android-publish.gradle

@@ -1,5 +1,5 @@
 /*
- * Copyright 2021 Cyface GmbH
+ * Copyright 2021-2024 Cyface GmbH
  *
  * This file is part of the Cyface Publish Plugin for Android.
  *
@@ -42,9 +42,9 @@ plugins {
 // Setup Javadoc and source tasks for all build variants.
 project.android.libraryVariants.all { variant ->
 
-    def javaDocDestDir = file("${buildDir}/docs/${variant.name}Javadoc")
+    def javaDocDestDir = layout.buildDirectory.dir("docs/${variant.name}Javadoc")
     def javadocTaskName = "${variant.name}Javadoc"
-    def javadoc = tasks.create(javadocTaskName, Javadoc) {
+    def javadoc = tasks.register(javadocTaskName, Javadoc) {
         description "Generates Javadoc for ${variant.name}."
         source = variant.javaCompileProvider.get().source
         destinationDir = javaDocDestDir