chore: update PR and issue template to use h2 (#10865)

.github/ISSUE_TEMPLATE.md

@@ -3,11 +3,11 @@ Before opening: please search existing issues to avoid duplicates, and confirm t
 For usage questions, please use Stack Overflow (https://stackoverflow.com/questions/tagged/axios) instead.
 -->
 
-#### Describe the issue
+## Describe the issue
 
 A clear description of the bug or feature request.
 
-#### Example code
+## Example code
 
 <!-- A minimal snippet that reproduces the issue. Remove any secrets/tokens. -->
 
@@ -15,15 +15,15 @@ A clear description of the bug or feature request.
 
 ```
 
-#### Expected behavior
+## Expected behavior
 
 What you expected to happen.
 
-#### Actual behavior
+## Actual behavior
 
 What actually happened (include error messages or stack traces if relevant).
 
-#### Environment
+## Environment
 
 - Axios version:
 - Adapter: <!-- xhr | http | fetch -->

.github/PULL_REQUEST_TEMPLATE.md

@@ -5,15 +5,15 @@ Thanks for contributing to axios! A few quick notes:
 - If you leave the description blank, our AI agent will draft one — feel free to edit afterwards.
 -->
 
-#### Summary
+## Summary
 
 <!-- What does this PR do, and why? -->
 
-#### Linked issue
+## Linked issue
 
 <!-- e.g. Closes #1234 -->
 
-#### Changes
+## Changes
 
 <!-- Bullet list of the notable changes. Keep it short. -->