fix switcher_json variable replacement

Author: M-Chan

template/{% if docs_type=="sphinx" %}docs{% endif %}/conf.py.jinja

@@ -128,7 +128,7 @@ copybutton_prompt_is_regexp = True
 html_theme = "pydata_sphinx_theme"
 github_repo = "{{ repo_name }}"
 github_user = "{{ github_org }}"
-switcher_json = f"https://{github_user}.github.io/{github_repo}/switcher.json"
+switcher_json = "https://{{ github_org }}.github.io/{{ repo_name }}/switcher.json"
 switcher_exists = requests.get(switcher_json).ok
 if not switcher_exists:
     print(