fix(runner): preserve fixtures when calling runif and skipif (fix #4585)

[dsyddall]

Description

Fixes #4585

Currently, calling test.runIf() and test.skipIf() does not propagate the test's context through the method chain. This causes test fixtures to become unavailable after calling runIf or skipIf. This PR fixes the issue by making the runIf and skipIf functions return the same instance of the test object instead of returning the base test object, preserving the test context.

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