[CI] Allow only one concurrent build of the same workflow at a time. Every new attempt to build should cancel already running build.

Author: vyazelenko

.github/workflows/ci.yml

@@ -8,6 +8,10 @@ on:
     branches:
       - master
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 env:
   GRADLE_OPTS: "-Dorg.gradle.daemon=false -Dorg.gradle.java.installations.auto-detect=false -Dorg.gradle.warning.mode=fail"
   CMAKE_VERSION: "3.6.1"