CI use 6.1 nightlies #20

Job	Run time
Cxx interop / Construct Cxx interop matrix	4s
Unit tests / Construct unit test matrix	3s
Soundness / API breakage check	0s
Soundness / Broken symlinks check	3s
Soundness / Documentation check	57s
Soundness / License headers check	5s
Soundness / Format check	32s
Soundness / Python lint check	8s
Soundness / Unacceptable language check	4s
Soundness / Shell check	38s
Soundness / YAML lint check	5s
Unit tests / Unit tests / Linux (5.9)	34s
Unit tests / Unit tests / Linux (5.10)	38s
Unit tests / Unit tests / Linux (6.0)	45s
Unit tests / Unit tests / Linux (nightly-6.1)	51s
Unit tests / Unit tests / Linux (nightly-main)	46s
Cxx interop / Cxx interop / Linux (5.9)	46s
Cxx interop / Cxx interop / Linux (5.10)	38s
Cxx interop / Cxx interop / Linux (6.0)	47s
Cxx interop / Cxx interop / Linux (nightly-6.1)	54s
Cxx interop / Cxx interop / Linux (nightly-main)	49s
	10m 7s

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