Enable release mode builds #71

Job	Run time
Construct Cxx interop matrix	6s
Unit tests / Unit tests (6.1)	4m 18s
Unit tests / Unit tests (6.0)	3m 6s
Unit tests / Unit tests (nightly-main)	4m 18s
Unit tests / Unit tests (5.9)	35s
Unit tests / Unit tests (nightly-6.1)	3m 0s
Release builds / Release builds (6.1)	2m 2s
Release builds / Release builds (6.0)	2m 18s
Release builds / Release builds (nightly-6.1)	2m 32s
Release builds / Release builds (5.10)	2m 9s
Unit tests / Unit tests (5.10)	2m 43s
Release builds / Release builds (nightly-main)	2m 26s
Release builds / Release builds (5.9)	34s
Soundness / Documentation check	1m 54s
Soundness / Unacceptable language check	8s
Soundness / License headers check	7s
Soundness / API breakage check	2m 11s
Soundness / Broken symlinks check	6s
Soundness / Format check	39s
Soundness / Shell check	35s
Soundness / YAML lint check	7s
Soundness / Python lint check	12s
Cxx interop / Linux (nightly-next)	1m 56s
Cxx interop / Linux (nightly-main)	1m 56s
Cxx interop / Linux (6.0)	1m 34s
Cxx interop / Linux (6.1)	1m 37s
Cxx interop / Linux (5.10)	1m 21s
	44m 30s

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