test: prevent storage directory leak from randomized env vars test

[vdusek]

Summary

• test_get_env_with_randomized_env_vars was overriding APIFY_LOCAL_STORAGE_DIR with a random 10-char string (e.g. KAHL8QER2W), causing Actor.init() to create a leftover storage directory in the project root on every test run
• Excluded LOCAL_STORAGE_DIR from randomization and set the expected value to the tmp_path provided by the _isolate_test_environment fixture

Test plan

• uv run poe lint passes
• uv run poe unit-tests passes (249 tests)
• No leftover directories created in the project root after test run

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.02%. Comparing base (56cfc38) to head (c2af53c).
⚠️ Report is 3 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (56cfc38) and HEAD (c2af53c). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (56cfc38)	HEAD (c2af53c)
integration	1	0

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #779       +/-   ##
===========================================
- Coverage   81.86%   68.02%   -13.84%     
===========================================
  Files          46       46               
  Lines        2696     2696               
===========================================
- Hits         2207     1834      -373     
- Misses        489      862      +373     

Flag	Coverage Δ
integration	?
unit	68.02% <ø> (ø)

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