Fixed warnings when -require-explicit-sendable is enabled #23

Job	Run time
Unit tests / Construct unit test matrix	3s
Static SDK / Construct Static SDK matrix	3s
Cxx interop / Construct Cxx interop matrix	2s
Release builds / Construct release build matrix	3s
Soundness / License headers check	2s
Soundness / Format check	3s
Soundness / Documentation check	2s
Soundness / Shell check	2s
Soundness / Unacceptable language check	4s
Soundness / API breakage check	2s
Soundness / YAML lint check	3s
Soundness / Python lint check	3s
Soundness / Broken symlinks check	3s
Cxx interop / Cxx interop	-1s
Release builds / Release builds	0s
Unit tests / Unit tests	0s
Static SDK / Static SDK	0s
	34s

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