Fix #10257. Clear resource warnings by using os.popen's context manager.

Lib/test/test_os.py

@@ -406,12 +406,14 @@ class EnvironTests(mapping_tests.BasicTestMappingProtocol):
         os.environ.clear()
         if os.path.exists("/bin/sh"):
             os.environ.update(HELLO="World")
-            value = os.popen("/bin/sh -c 'echo $HELLO'").read().strip()
+            with os.popen("/bin/sh -c 'echo $HELLO'") as popen:
+                value = popen.read().strip()
                 self.assertEquals(value, "World")
 
     def test_os_popen_iter(self):
         if os.path.exists("/bin/sh"):
-            popen = os.popen("/bin/sh -c 'echo \"line1\nline2\nline3\"'")
+            with os.popen(
+                "/bin/sh -c 'echo \"line1\nline2\nline3\"'") as popen:
                 it = iter(popen)
                 self.assertEquals(next(it), "line1\n")
                 self.assertEquals(next(it), "line2\n")