Fix redirect when using lowercase reponame (#18775)

* Previously,  `GET {username}/{reponame}/raw///file-path` (the middle two slashes are blank to get the default branch) when the repo name has uppercase letters, e.g., https://try.gitea.io/AbdulrhmnGhanem/CH330_Hardware, using a lowercase version of the name redirected to the correct URL
* In other words both
   * `GET https://try.gitea.io/AbdulrhmnGhanem/CH330_Hardware/raw///images/back.png`
   * `GET https://try.gitea.io/AbdulrhmnGhanem/ch330_hardware/raw///images/back.png`
were redirecting to ` GET https://try.gitea.io/AbdulrhmnGhanem/CH330_Hardware/raw/branch/master/images/back.png`
This isn't the case after  #17551. Specifically because of this [line](cbd5eecd14/modules/context/repo.go (L860)).

modules/context/repo.go

@@ -914,7 +914,7 @@ func RepoRefByType(refType RepoRefType, ignoreNotExistErr ...bool) func(*Context
 
 			if refType == RepoRefLegacy {
 				// redirect from old URL scheme to new URL scheme
-				prefix := strings.TrimPrefix(setting.AppSubURL+strings.TrimSuffix(ctx.Req.URL.Path, ctx.Params("*")), ctx.Repo.RepoLink)
+				prefix := strings.TrimPrefix(setting.AppSubURL+strings.ToLower(strings.TrimSuffix(ctx.Req.URL.Path, ctx.Params("*"))), strings.ToLower(ctx.Repo.RepoLink))
 
 				ctx.Redirect(path.Join(
 					ctx.Repo.RepoLink,