konflux: arm64 build

Signed-off-by: Haoyu Sun <hasun@redhat.com>

Author: raptorsun

.tekton/lightspeed-stack-pull-request.yaml

@@ -31,6 +31,7 @@ spec:
   - name: build-platforms
     value:
     - linux/x86_64
+    - linux-c6gd2xlarge/arm64
   # todo: change on-push pipeline,too
   - name: build-source-image
     value: 'true'

.tekton/lightspeed-stack-push.yaml

@@ -28,6 +28,7 @@ spec:
   - name: build-platforms
     value:
     - linux/x86_64
+    - linux-c6gd2xlarge/arm64
   - name: build-source-image
     value: 'true'
   - name: prefetch-input