gh-148919: Make test_redirect_no_path independent of proxy environment variables (#148920)

* gh-148919: Make test_redirect_no_path independent of proxy environment variables

* gh-148919: Also make test_redirect_encoding independent of proxy env

test_redirect_encoding uses build_opener(), which installs the default
ProxyHandler, so it failed the same way when http_proxy was set.  Move
the environment cleanup into a helper and use EnvironmentVarGuard.unset().

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Senthil Kumaran <senthil@python.org>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

Author: 3 people

Lib/test/test_urllib2.py

@@ -1453,8 +1453,15 @@ def test_redirect_fragment(self):
         fp = o.open('http://www.example.com')
         self.assertEqual(fp.geturl(), redirected_url.strip())
 
+    def unset_proxy_env(self):
+        # Keep the test independent from proxy-related environment settings.
+        env = self.enterContext(os_helper.EnvironmentVarGuard())
+        env.unset("http_proxy", "https_proxy", "all_proxy", "no_proxy",
+                  "HTTP_PROXY", "HTTPS_PROXY", "ALL_PROXY", "NO_PROXY")
+
     def test_redirect_no_path(self):
         # Issue 14132: Relative redirect strips original path
+        self.unset_proxy_env()
 
         # clear _opener global variable
         self.addCleanup(urllib.request.urlcleanup)
@@ -1488,6 +1495,7 @@ def http_open(self, req):
                     b'123'
                 )
                 return result
+        self.unset_proxy_env()
         handler = Handler()
         opener = urllib.request.build_opener(handler)
         tests = (