CI use 6.1 nightlies #56

Job	Run time
Cxx interop / Construct Cxx interop matrix	3s
Unit tests / Construct unit test matrix	3s
Soundness / API breakage check	3m 16s
Soundness / Documentation check	2m 19s
Soundness / Broken symlinks check	3s
Soundness / Format check	35s
Soundness / License headers check	5s
Soundness / Shell check	36s
Soundness / Python lint check	5s
Soundness / YAML lint check	2s
Soundness / Unacceptable language check	3s
Cxx interop / Cxx interop / Linux (5.9)	1m 57s
Cxx interop / Cxx interop / Linux (5.10)	1m 54s
Cxx interop / Cxx interop / Linux (6.0)	2m 10s
Cxx interop / Cxx interop / Linux (nightly-6.1)	2m 39s
Cxx interop / Cxx interop / Linux (nightly-main)	2m 36s
Unit tests / Unit tests / Linux (5.9)	4m 7s
Unit tests / Unit tests / Linux (5.10)	4m 11s
Unit tests / Unit tests / Linux (6.0)	4m 32s
Unit tests / Unit tests / Linux (nightly-6.1)	4m 57s
Unit tests / Unit tests / Linux (nightly-main)	4m 56s
	41m 9s

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