Increase timeout threshold for linkcheck tests

[jayaddison]

Feature or Bugfix

• Bugfix (for flaky tests)

Purpose

• Increases the timeout threshold for the linkcheck builder tests from 0.05s to 0.075s
• Resolves Flaky unit tests: linkcheck builder (tests/test_build_linkcheck.py) #11299

Detail

• The performance of the linkcheck tests was improved a few weeks ago (97f07ca)
• That introduced some improved (lower) timeout thresholds that had to be adjusted a little (7d928b3)
• A few failures remained, and that resulted in me opening issue Flaky unit tests: linkcheck builder (tests/test_build_linkcheck.py) #11299
• I think that the changes here should allow the flaky tests to pass consistently
• I haven't been able to find any other reason that performance would have degraded for these tests recently

Relates

• Should fix Flaky unit tests: linkcheck builder (tests/test_build_linkcheck.py) #11299.