Adjust changelog for v1.21.6 to move prs to correct labels (#29339) (#29343)

When releasing, the releaser should read all the pull requests carefully
and do some adjustments because some of pull requests' labels are not
right when it's merged.

And the changelog tool needs to be adjusted. If one pull request has
both `bug` and `API`, it should mark it as `bug` but not `API`.

Backport #29339

CHANGELOG.md

@@ -9,9 +9,6 @@ been added to each release, please refer to the [blog](https://blog.gitea.com).
 * SECURITY
   * Fix XSS vulnerabilities (#29336)
   * Use general token signing secret (#29205) (#29325)
-* API
-  * Refactor issue template parsing and fix API endpoint (#29069) (#29140)
-  * Fix swift packages not resolving (#29095) (#29102)
 * ENHANCEMENTS
   * Refactor git version functions and check compatibility (#29155) (#29157)
   * Improve user experience for outdated comments (#29050) (#29086)
@@ -19,7 +16,11 @@ been added to each release, please refer to the [blog](https://blog.gitea.com).
   * Wrap contained tags and branches again (#29021) (#29026)
   * Fix incorrect button CSS usages (#29015) (#29023)
   * Strip trailing newline in markdown code copy (#29019) (#29022)
+  * Implement some action notifier functions (#29173) (#29308)
+  * Load outdated comments when (un)resolving conversation on PR timeline (#29203) (#29221)
 * BUGFIXES
+  * Refactor issue template parsing and fix API endpoint (#29069) (#29140)
+  * Fix swift packages not resolving (#29095) (#29102)
   * Remove SSH workaround (#27893) (#29332)
   * Only log error when tag sync fails (#29295) (#29327)
   * Fix SSPI user creation (#28948) (#29323)
@@ -44,18 +45,15 @@ been added to each release, please refer to the [blog](https://blog.gitea.com).
   * Avoid showing unnecessary JS errors when there are elements with different origin on the page (#29081) (#29089)
   * Fix gitea-origin-url with default ports (#29085) (#29088)
   * Fix orgmode link resolving (#29024) (#29076)
-  * Fix: Elasticsearch: Request Entity Too Large #28117 (#29062) (#29075)
+  * Fix Elasticsearh Request Entity Too Large #28117 (#29062) (#29075)
   * Do not render empty comments (#29039) (#29049)
   * Avoid sending update/delete release notice when it is draft (#29008) (#29025)
-* DOCS
-  * Rm outdated docs from some languages (#27530) (#29208)
-* MISC
-  * Implement some action notifier functions (#29173) (#29308)
   * Fix gitea-action user avatar broken on edited menu (#29190) (#29307)
   * Disallow merge when required checked are missing (#29143) (#29268)
-  * Convert visibility to number (#29226) (#29244)
-  * Load outdated comments when (un)resolving conversation on PR timeline (#29203) (#29221)
   * Fix incorrect link to swift doc and swift package-registry login command (#29096) (#29103)
+  * Convert visibility to number (#29226) (#29244)
+* DOCS
+  * Remove outdated docs from some languages (#27530) (#29208)
   * Fix typos in the documentation (#29048) (#29056)
   * Explained where create issue/PR template (#29035)
 
@@ -174,7 +172,7 @@ been added to each release, please refer to the [blog](https://blog.gitea.com).
   * Fix Chinese translation of config cheat sheet[API] (#28472) (#28473)
   * Retry SSH key verification with additional CRLF if it failed (#28392) (#28464)
 
-## [1.21.2](https://github.com/go-gitea/gitea/releases/tag/1.21.2) - 2023-12-12
+## [1.21.2](https://github.com/go-gitea/gitea/releases/tag/v1.21.2) - 2023-12-12
 
 * SECURITY
   * Rebuild with recently released golang version
@@ -213,7 +211,7 @@ been added to each release, please refer to the [blog](https://blog.gitea.com).
   * Use full width for project boards (#28225) (#28245)
   * Enable system users search via the API (#28013) (#28018)
 
-## [1.21.1](https://github.com/go-gitea/gitea/releases/tag/1.21.1) - 2023-11-26
+## [1.21.1](https://github.com/go-gitea/gitea/releases/tag/v1.21.1) - 2023-11-26
 
 * SECURITY
   * Fix comment permissions (#28213) (#28216)