Testsuite: Support interceptors in child workflows mocks

[seriousben]

What changed? Adding the missing interceptors in the workflow context sent to child workflow mocks.

Why? To support calling workflow.GetInfo(ctx) within mocks without a panic.

This is a regression introduced in 0.12.2 as part of adding interceptor support.

How did you test it?

• [x] Unit tested
• [x] Tested locally

Unit test failure before the fix:

panic: getWorkflowInterceptor: Not a workflow context

goroutine 47 [running]:
go.uber.org/cadence/internal.getWorkflowInterceptor(...)
    cadence-client/internal/internal_workflow.go:288
go.uber.org/cadence/internal.GetWorkflowInfo(0x1aec9c0, 0xc0004fe000, 0xc0004fe000)
    cadence-client/internal/workflow.go:756 +0xce
go.uber.org/cadence/internal.(*WorkflowTestSuiteUnitTest).Test_ChildWorkflow_Mock.func2(0xc00007ed80, 0x3, 0x4)
    cadence-client/internal/internal_workflow_testsuite_test.go:728 +0x7d

Potential risks No risk since only changing the testsuite.

[coveralls]

Pull Request Test Coverage Report for Build 4bbb5de7-00c2-420d-8d5d-10d33ababfb2

• 5 of 5 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 74.753%

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Totals
Change from base Build a491e373-0128-45c3-aa5f-a91cb5150fe3:	0.02%
Covered Lines:	9593
Relevant Lines:	12833

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💛 - Coveralls