[Doc] Convert docs to use colon fences (#12471)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

docs/source/contributing/overview.md

@@ -35,17 +35,17 @@ pre-commit run --all-files
 pytest tests/
 ```
 
-```{note}
+:::{note}
 Currently, the repository is not fully checked by `mypy`.
-```
+:::
 
 ## Issues
 
 If you encounter a bug or have a feature request, please [search existing issues](https://github.com/vllm-project/vllm/issues?q=is%3Aissue) first to see if it has already been reported. If not, please [file a new issue](https://github.com/vllm-project/vllm/issues/new/choose), providing as much relevant information as possible.
 
-```{important}
+:::{important}
 If you discover a security vulnerability, please follow the instructions [here](gh-file:SECURITY.md#reporting-a-vulnerability).
-```
+:::
 
 ## Pull Requests & Code Reviews
 
@@ -81,9 +81,9 @@ appropriately to indicate the type of change. Please use one of the following:
 - `[Misc]` for PRs that do not fit the above categories. Please use this
   sparingly.
 
-```{note}
+:::{note}
 If the PR spans more than one category, please include all relevant prefixes.
-```
+:::
 
 ### Code Quality