update to 28.1.0 (#578)

Bump the v28 docs to the 28.1.0 release, following the 1.27.3 bump (#532):

- point the `28` version variables (`version`, `sourceVersion`, `dockerVersion`, `displayVersion`) at 28.1.0
- update the v28 entry in `update_api_docs.sh` to `28.1.0`
- regenerate `static/swagger-28.json` and `static/openapi3-28.json` from the `v28.1.0` tag

---------

Co-authored-by: Lunny Xiao <[email protected]>
Reviewed-on: https://gitea.com/gitea/docs/pulls/578
Reviewed-by: TheFox0x7 <[email protected]>
Co-authored-by: bircni <[email protected]>

static/openapi3-28.json

@@ -11119,7 +11119,7 @@
       "url": "http://opensource.org/licenses/MIT"
     },
     "title": "Gitea API",
-    "version": "28.0.0"
+    "version": "28.1.0"
   },
   "openapi": "3.0.3",
   "paths": {

static/swagger-28.json

@@ -17,7 +17,7 @@
       "name": "MIT",
       "url": "http://opensource.org/licenses/MIT"
     },
-    "version": "28.0.0"
+    "version": "28.1.0"
   },
   "basePath": "https://gitea.com/api/v1",
   "paths": {