Fix json_url, kind of... see pydata/pydata-sphinx-theme#1389

docs/conf.py

@@ -210,19 +210,19 @@ def setup(app):
 json_url = "https://ctapipe.readthedocs.io/en/latest/_static/switcher.json"
 
 # Define the version we use for matching in the version switcher.
-version_match = os.environ.get("READTHEDOCS_VERSION")
+version_match = os.getenv("READTHEDOCS_VERSION")
 # If READTHEDOCS_VERSION doesn't exist, we're not on RTD
 # If it is an integer, we're in a PR build and the version isn't correct.
 if not version_match or version_match.isdigit():
     # For local development, infer the version to match from the package.
     if "dev" in release or "rc" in release:
         version_match = "latest"
-        # We want to keep the relative reference if we are in dev mode
-        # but we want the whole url if we are effectively in a released version
-        json_url = "/_static/switcher.json"
     else:
         version_match = release
 
+    # We want to keep the relative reference when on a pull request or locally
+    json_url = "_static/switcher.json"
+
 
 # -- Options for HTML output ----------------------------------------------