Add autocancellation of the stale PR GHA jobs

Author: webknjaz

.github/workflows/test-library.yml

@@ -2,6 +2,15 @@ name: Proxy.py Library
 
 on: [push, pull_request]
 
+concurrency:
+  group: >-
+    ${{
+        github.workflow
+    }}-${{
+        github.event.pull_request.number || github.sha
+    }}
+  cancel-in-progress: true
+
 jobs:
   build:
     runs-on: ${{ matrix.os }}-latest