Include pending status on PR's under test

Note, this does an implicit-get. If you wanted to avoid the extra
"get" of the resource, this GitHub Issue provides a workaround:
telia-oss/github-pr-resource#32

[#163883149]

Author: bwasmith

ci/cli-pr-builder/pipeline.yml

@@ -59,6 +59,10 @@ jobs:
       trigger: true
     - get: cli-master
   - aggregate:
+    - put: cli-pr
+      params:
+        path: cli-pr
+        status: pending
     - task: units-linux
       timeout: 30m
       input_mapping: