CI: docs: Remove explicit Nim version requiremetn.

Author: moigagoo

.github/workflows/docs.yml

@@ -21,8 +21,6 @@ jobs:
 
       - name: Setup Nim
         uses: jiro4989/setup-nim-action@v2
-        with:
-          nim-version: 2.2.6
 
       - name: Build docs
         run: nimble docs