Fix list of proposed kind/ labels for PRs

kind/failing-test is not supported kind label at this moment, so better
to remove if from the list with suggested labels to avoid error in
check-pr-has-kind-label job.

Signed-off-by: Yulia Gaponenko <yulia.gaponenko1@de.ibm.com>

.github/pull_request_template.md

@@ -9,7 +9,7 @@ In addition, categorize the changes you're making using the "/kind" Prow command
 
 /kind <kind>
 
-Supported kinds are: bug, cleanup, design, documentation, failing-test, feature, flake, misc, question, tep
+Supported kinds are: bug, cleanup, design, documentation, feature, flake, misc, question, tep
 -->
 
 # Submitter Checklist