ci: Specify concurrency for github workflows (#2059)

.github/workflows/check_libxrpl.yml

@@ -4,6 +4,11 @@ on:
   repository_dispatch:
     types: [check_libxrpl]
 
+concurrency:
+  # Only cancel in-progress jobs or runs for the current workflow - matches against branch & tags
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 env:
   CONAN_PROFILE: gcc