Downgrade to Gradle 6.8.3 as Gradle 7.0 has problems with the screenshots task, add caching in workflow

.github/workflows/generate-screenshots.yml

@@ -18,6 +18,16 @@ jobs:
           echo $LD_LIBRARY_PATH
           export GALLIUM_DRIVER=swr
           xvfb-run glxinfo
+
+      - uses: actions/cache@v2
+        with:
+          path: |
+            ~/.gradle/caches
+            ~/.gradle/wrapper
+          key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle*', '**/gradle-wrapper.properties') }}
+          restore-keys: |
+            ${{ runner.os }}-gradle-
+
       - name: Collect screenshots
         run: xvfb-run ./gradlew collectScreenshots
       - name: Build main readme

build.gradle

@@ -19,7 +19,7 @@ apply plugin: 'org.jetbrains.dokka'
 
 project.ext {
     openrndrVersion = openrndrUseSnapshot? "0.4.0-SNAPSHOT" : "0.3.47"
-    kotlinVersion = "1.4.31"
+    kotlinVersion = "1.4.32"
     spekVersion = "2.0.15"
     libfreenectVersion = "0.5.7-1.5.5"
     librealsense2Version = "2.40.0-1.5.5"
@@ -221,6 +221,7 @@ task collectScreenshots {
                             def klass = ucl.loadClass(klassName)
                             try {
                                 def mainMethod = klass.getMethod("main")
+                                println "Collecting screenshot for ${klassName}"
                                 javaexec {
                                     classpath set.runtimeClasspath
                                     def className = y.name.replace(".class", "")

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-7.0-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.8.3-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists