gh-129192: Use EnvironmentVarGuard to restore environment variables

[Eclips4]

• Issue: test_zipfile fails (env changed) #129192

[Eclips4]

Previously:

eclips4@nixos ~/p/p/cpython (main)> ./python -m test -q test_zipfile
Using random seed: 315532800
0:00:00 load avg: 2.32 Run 1 test sequentially in a single process
test_zipfile failed (env changed)

== Tests result: SUCCESS ==

1 test altered the execution environment (env changed):
    test_zipfile


Total duration: 19.2 sec
Total tests: run=338 skipped=5
Total test files: run=1/1
Result: SUCCESS

With this patch applied:

eclips4@nixos ~/p/p/cpython (fix-test-zipfile)> ./python -m test -q test_zipfile
Using random seed: 315532800
0:00:00 load avg: 1.77 Run 1 test sequentially in a single process

== Tests result: SUCCESS ==

Total duration: 19.9 sec
Total tests: run=338 skipped=5
Total test files: run=1/1
Result: SUCCESS