ci: add concurrency settings to cancel redundant workflow runs

Adds a concurrency block to kind-e2e.yaml and knative-downstream.yaml
so that pushing a new commit to a PR cancels any in-progress run for
the same ref, avoiding wasted runner minutes on the expensive
3-suite × 2-k8s-version e2e matrix.

Author: Ankitsinghsisodya

.github/workflows/kind-e2e.yaml

@@ -8,6 +8,10 @@ defaults:
   run:
     shell: bash
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
 
   e2e-tests:

.github/workflows/knative-downstream.yaml

@@ -18,6 +18,10 @@ on:
   pull_request:
     branches: [ 'main', 'master' ]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
 
   downstream-knative: