fix bug and feature issue templates (#5493)

* Update 02_feature_request.yml

* Update 01_bug_report.yml

* Update 03_docs.yml

Author: ndonkoHenri

.github/ISSUE_TEMPLATE/01_bug_report.yml

@@ -1,8 +1,7 @@
----
 name: Bug Report
 description: "You found a bug in Flet causing your application to crash or behave abnormally? Help us know more about it by providing as much details as possible."
-labels: bug
----
+title: "bug: "
+labels: ["bug"]
 
 body:
   - type: markdown

.github/ISSUE_TEMPLATE/02_feature_request.yml

@@ -1,9 +1,7 @@
----
 name: Feature Request
 description: "Suggest a new feature to be added to Flet."
 title: "feature: "
-labels: feature request
----
+labels: ["feature request"]
 
 body:
   - type: checkboxes

.github/ISSUE_TEMPLATE/03_docs.yml

@@ -1,9 +1,7 @@
----
 name: Documentation update
 about: Found some unclear, missing or outdated documentation?
 title: "docs: "
-labels: documentation
----
+labels: ["documentation"]
 
 body:
   - type: textarea