minor PHP-CS-Fixer#5023 Fix issue templates (kubawerlos)

This PR was merged into the 2.15 branch.

Discussion
----------

Fix issue templates

Must be [`labels`](https://raw.githubusercontent.com/sebastianbergmann/phpunit/9.2.4/.github/ISSUE_TEMPLATE/BUG.md), not `label` to work :)

Commits
-------

ca392eb Fix issue templates

.github/ISSUE_TEMPLATE/bug_report.md

@@ -1,7 +1,7 @@
 ---
 name: Bug report 🐛
 about: Existing feature does not behave as expected.
-label: kind/bug
+labels: kind/bug
 ---
 
 ## Bug report

.github/ISSUE_TEMPLATE/feature_request.md

@@ -1,7 +1,7 @@
 ---
 name: Feature request 🚀
 about: I have a suggestion about a new feature (and may want to implement it)!
-label: kind/feature request
+labels: kind/feature request
 ---
 
 ## Feature request

.github/ISSUE_TEMPLATE/rule_request.md

@@ -1,7 +1,7 @@
 ---
 name: Rule request ✍️
 about: I have a suggestion about a new rule (and may want to implement it)!
-label: kind/feature request
+labels: kind/feature request
 ---
 
 ## Rule request

.github/ISSUE_TEMPLATE/support_question.md

@@ -1,7 +1,7 @@
 ---
 name: Support question ❓
 about: You have a question about how the tool works or how to use it.
-label: kind/question
+labels: kind/question
 ---
 
 ## Support question