test: raise call_with_exp_backoff retry budget for flaky shared RQ tests

[vdusek]

Description

test_request_ordering_with_mixed_operations[shared] failed on CI because fetch_next_request returned None after all retries. The test already wraps the call in call_with_exp_backoff, but the helper's default max_retries=3 only allows 1+2+4 = 7s of backoff — shared RQ propagation delay (see #808) occasionally exceeds that.

Raising the default to max_retries=5 extends the worst-case wait to 1+2+4+8+16 = 31s. No cost in the happy path (returns on the first successful call), and the change benefits all 37 call sites of the helper.

Failed CI run: https://github.com/apify/apify-sdk-python/actions/runs/24673724360/job/72151584275

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.64%. Comparing base (737b0dd) to head (d117f3a).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #876      +/-   ##
==========================================
+ Coverage   86.57%   86.64%   +0.06%     
==========================================
  Files          48       48              
  Lines        2920     2920              
==========================================
+ Hits         2528     2530       +2     
+ Misses        392      390       -2     

Flag	Coverage Δ
e2e	37.87% <ø> (ø)
integration	59.28% <ø> (ø)
unit	75.37% <ø> (+0.06%)	⬆️

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