Relax constraint on Wiki IDs, since subdirectories can contain spaces

If a subdirectory contains spaces, GitLab would be unable to generate
the route in the sidebar, resulting in an Error 500.

Closes #30357

changelogs/unreleased/sh-relax-wiki-slug-constraint.yml

@@ -0,0 +1,4 @@
+---
+title: Relax constraint on Wiki IDs, since subdirectories can contain spaces
+merge_request:
+author:

config/routes/wiki.rb

@@ -1,5 +1,3 @@
-WIKI_SLUG_ID = { id: /\S+/ }.freeze unless defined? WIKI_SLUG_ID
-
 scope(controller: :wikis) do
   scope(path: 'wikis', as: :wikis) do
     get :git_access
@@ -8,7 +6,7 @@ scope(controller: :wikis) do
     post '/', to: 'wikis#create'
   end
 
-  scope(path: 'wikis/*id', as: :wiki, constraints: WIKI_SLUG_ID, format: false) do
+  scope(path: 'wikis/*id', as: :wiki, format: false) do
     get :edit
     get :history
     post :preview_markdown