Branch name must be URL encoded

What does this MR do and why?

For the API to Get single repository branch, the name of the branch may have to be url encoded.

Screenshots or screen recordings

N/A.

How to set up and validate locally

curl --header "PRIVATE-TOKEN: <your_access_token>" "https://gitlab.example.com/api/v4/projects/5/repository/branches/bug/mybugfix" gives this errorL {"error":"404 Not Found"} but curl --header "PRIVATE-TOKEN: <your_access_token>" "https://gitlab.example.com/api/v4/projects/5/repository/branches/bug%2Fmybugfix" works.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

doc/api/branches.md

@@ -84,7 +84,7 @@ Parameters:
 | Attribute | Type           | Required | Description                                                                                                  |
 |:----------|:---------------|:---------|:-------------------------------------------------------------------------------------------------------------|
 | `id`      | integer/string | yes      | ID or [URL-encoded path of the project](index.md#namespaced-path-encoding) owned by the authenticated user. |
-| `branch`  | string         | yes      | Name of the branch.                                                                                          |
+| `branch`  | string         | yes      | [URL-encoded name](index.md#namespaced-path-encoding) of the branch.                                                                                          |
 
 Example request: