Improve path_to_url() tests

Use `urllib.parse.quote()` rather than `urllib.request.pathname2url()` to
generate expected URLs in tests for `path_to_url()`. This makes
expectations a little more explicit.

(The implementation of `path_to_url()` itself calls `pathname2url()`, and
so we were marking our own homework!)

Author: barneygale

news/7dab557a-8fb5-41c5-afae-a92c8ab02aba.trivial.rst

@@ -1,6 +1,6 @@
 import os
 import sys
-import urllib.request
+import urllib.parse
 
 import pytest
 
@@ -11,7 +11,7 @@
 def test_path_to_url_unix() -> None:
     assert path_to_url("/tmp/file") == "file:///tmp/file"
     path = os.path.join(os.getcwd(), "file")
-    assert path_to_url("file") == "file://" + urllib.request.pathname2url(path)
+    assert path_to_url("file") == "file://" + urllib.parse.quote(path)
 
 
 @pytest.mark.skipif("sys.platform != 'win32'")
@@ -38,8 +38,9 @@ def test_unc_path_to_url_win() -> None:
 
 @pytest.mark.skipif("sys.platform != 'win32'")
 def test_relative_path_to_url_win() -> None:
-    resolved_path = os.path.join(os.getcwd(), "file")
-    assert path_to_url("file") == "file:" + urllib.request.pathname2url(resolved_path)
+    resolved_path = os.path.join(os.getcwd(), "file").replace("\\", "/")
+    quoted_path = urllib.parse.quote(resolved_path, safe="/:")
+    assert path_to_url("file") == "file:///" + quoted_path
 
 
 @pytest.mark.parametrize(