docs: fix examples for RequestBody (#2415)

Hi,

this is my first try with this bundle and I got into an error that leads
me to a discussion on github. Following the discussion here:
#1990 (comment)
I think that the documentation should be updated to match the "content"
argument.
But maybe I've missed something else ?

Thanks !

## What type of PR is this? (check all applicable)
- [ ] Bug Fix
- [ ] Feature
- [ ] Refactor
- [ ] Deprecation
- [ ] Breaking Change
- [x] Documentation Update
- [ ] CI

## Checklist
- [x] I have made corresponding changes to the documentation (`docs/`)
- [ ] I have made corresponding changes to the changelog
(`CHANGELOG.md`)

Co-authored-by: Djordy Koert <[email protected]>

docs/index.rst

@@ -389,10 +389,10 @@ that property type to not be nullable, for example.
         #[OA\Response(response: 200, content: new Model(type: UserDto::class, groups: ["default"]))]
 
         // Similarly, this will make the username `required` in the create  schema
-        #[OA\RequestBody(new Model(type: UserDto::class, groups: ["create"]))]
+        #[OA\RequestBody(content: new Model(type: UserDto::class, groups: ["create"]))]
 
         // But for updates, the `username` property will not be required
-        #[OA\RequestBody(new Model(type: UserDto::class, groups: ["update"]))]
+        #[OA\RequestBody(content: new Model(type: UserDto::class, groups: ["update"]))]
 
 
 .. tip::