Update Gradle CI script for UI tests and test execution

Change Xvfb screen depth to 24-bit for better compatibility and added a delay to ensure proper initialization. Updated test execution step to set DISPLAY environment variable on Ubuntu.

Author: VitaliyBoyko

.github/workflows/gradle.yml

@@ -18,7 +18,8 @@ jobs:
           - os: ubuntu-latest
             runIde: |
               export DISPLAY=:99.0
-              Xvfb -ac :99 -screen 0 1920x1080x16 &
+              Xvfb -ac :99 -screen 0 1920x1080x24 &
+              sleep 10
               ./gradlew runIdeForUiTests &
           - os: windows-latest
             runIde: start gradlew.bat runIdeForUiTests
@@ -56,7 +57,9 @@ jobs:
 
       # Run tests
       - name: Tests
-        run: ./gradlew test
+        run: |
+          export DISPLAY=:99.0
+          ./gradlew test
 
       - name: Capture Test Artifacts on Failure
         if: failure() && matrix.os == 'ubuntu-latest'