bugfix: github: Adjust label yaml quoting syntax.

Prior to this, two templates were ignored due to syntax errors.

Documentation suggests using quotes around all of labels, ie.
including commas inside the quote.
eg. https://github.com/orgs/community/discussions/23682

Labels with spaces and commas were already surrounded by quotes; this
change quotes labels in each template, and includes a comma at the end
inside the closing quote.

.github/ISSUE_TEMPLATE/01_crash.md

@@ -1,7 +1,7 @@
 ---
 name: Bug report (major)
 about: A major bug which significantly impacts usability, eg. an unexpected quit, crash, freeze.
-labels: 'bug: crash',
+labels: 'bug: crash,'
 ---
 
 ### Bug description

.github/ISSUE_TEMPLATE/02_bug.md

@@ -1,7 +1,7 @@
 ---
 name: Bug report
 about: A concrete bug report with steps to reproduce the behavior.
-labels: bug,
+labels: 'bug,'
 ---
 
 ### Bug description

.github/ISSUE_TEMPLATE/03_parity.md

@@ -1,7 +1,7 @@
 ---
 name: Feature request (a missing known Zulip feature)
 about: A request for a feature which is missing, but present in another Zulip client (eg. Web/Desktop/mobile).
-labels: 'missing feature',
+labels: 'missing feature,'
 ---
 
 ### Description of feature missing from another Zulip client

.github/ISSUE_TEMPLATE/04_platform.md

@@ -1,7 +1,7 @@
 ---
 name: Feature suggestion
 about: A suggestion for an improvement, specific to the capabilities of the terminal environment.
-labels: enhancement,
+labels: 'enhancement,'
 ---
 
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