Merge pull request #1307 from fluxcd/backport-release-v1.2.x-label

add `backport:release/v1.2.x` label

Author: aryan9600

.github/labels.yaml

@@ -22,3 +22,6 @@
 - name: backport:release/v1.1.x
   description: To be backported to release/v1.1.x
   color: '#ffd700'
+- name: backport:release/v1.2.x
+  description: To be backported to release/v1.2.x
+  color: '#ffd700'