Fix Python3.13 compatibility regarding urllib.parse module

Python 3.13 fixed handling relative paths in urllib.parse module.
Specifically, relative file URL is now constructed as file:path instead
of converting it to absolute file:///path. This breaks
salt.utils.url.create which expects file:/// specifically. The mismatch
results in for example changing salt://top.sls into salt://.sls and thus
not finding the top file.

Fix this by handling both prefixes.

Relevant python change: python/cpython#85110
Fixes: saltstack#66898

changelog/66898.fixed.md

@@ -0,0 +1 @@
+Fixed Python 3.13 compatibility regarding urllib.parse module

salt/utils/url.py

@@ -47,7 +47,7 @@ def create(path, saltenv=None):
 
     query = f"saltenv={saltenv}" if saltenv else ""
     url = salt.utils.data.decode(urlunparse(("file", "", path, "", query, "")))
-    return "salt://{}".format(url[len("file:///") :])
+    return f'salt://{re.sub(r"^file:/*", "", url)}'
 
 
 def is_escaped(url):