[release/5.0] Skip some PKCS9 tests on NetFx

[github-actions]

Backport of #45199 to release/5.0

/cc @GrabYourPitchforks

Notes

Servicing approved. No shipping product changes, just unit test changes.

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Issue Details

---

Backport of #45199 to release/5.0

/cc @GrabYourPitchforks

Customer Impact

Testing

Risk

Author:	github-actions[bot]
Assignees:	-
Labels:	area-System.Security
Milestone:	-

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Because this pull request has the auto-merge label, I will be glad to assist with helping to merge this pull request once all check-in policies pass.

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[GrabYourPitchforks]

• Unit test failure is known flaky test Timeout_SetTenMillisecondsOnLoopback_ThrowsWebException is sometimes failing with Assert.InRange() Failure #44494 (fixed in master, not in release/5.0)
• Unit test failure is known flaky test ConnectAsync_CancellationRequestedAfterConnect_ThrowsOperationCanceledException #41511

[ghost]

Apologies, while this PR appears ready to be merged, I've been configured to only merge when all checks have explicitly passed. The following integrations have not reported any progress on their checks and are blocking auto-merge:

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3. Dependabot

These integrations are possibly never going to report a check, and unblocking auto-merge likely requires a human being to update my configuration to exempt these integrations from requiring a passing check.

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