Don't hold a lock over a continuation in test helpers #207

Job	Run time
Unit tests / Construct unit test matrix	5s
Cxx interop / Construct Cxx interop matrix	6s
Release builds / Construct release build matrix	4s
Static SDK / Construct Static SDK matrix	7s
Soundness / Unacceptable language check	8s
Soundness / License headers check	9s
Soundness / Shell check	52s
Soundness / Format check	45s
Soundness / Broken symlinks check	5s
Soundness / API breakage check	5m 22s
Soundness / Documentation check	4m 4s
Soundness / Python lint check	9s
Soundness / YAML lint check	6s
Unit tests / Unit tests / Linux (6.0)	5m 51s
Unit tests / Unit tests / Linux (nightly-next)	6m 23s
Unit tests / Unit tests / Linux (6.1)	5m 38s
Unit tests / Unit tests / Linux (6.2)	5m 5s
Unit tests / Unit tests / Linux (nightly-main)	6m 22s
Release builds / Release builds / Linux (6.2)	3m 41s
Release builds / Release builds / Linux (6.1)	3m 59s
Release builds / Release builds / Linux (6.0)	4m 12s
Release builds / Release builds / Linux (nightly-next)	5m 20s
Release builds / Release builds / Linux (nightly-main)	4m 39s
Cxx interop / Cxx interop / Linux (6.2)	4m 6s
Cxx interop / Cxx interop / Linux (6.1)	3m 20s
Cxx interop / Cxx interop / Linux (nightly-next)	4m 21s
Cxx interop / Cxx interop / Linux (6.0)	6m 41s
Cxx interop / Cxx interop / Linux (nightly-main)	4m 20s
Static SDK / Static SDK / Linux (latest-release Jammy)	9m 22s
Static SDK / Static SDK / Linux (main Jammy)	11m 57s
	1h 47m 19s

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