Rename nightly_6_1 params to nightly_next #26

Job	Run time
Cxx interop / Construct Cxx interop matrix	2s
Unit tests / Construct unit test matrix	3s
Soundness / Documentation check	2m 56s
Soundness / API breakage check	4m 39s
Soundness / Broken symlinks check	4s
Soundness / Format check	30s
Soundness / License headers check	3s
Soundness / Shell check	36s
Soundness / Unacceptable language check	3s
Soundness / Python lint check	7s
Soundness / YAML lint check	3s
Cxx interop / Swift 6 language mode	2m 34s
Cxx interop / Cxx interop / Linux (5.9)	2m 38s
Cxx interop / Cxx interop / Linux (5.10)	2m 34s
Cxx interop / Cxx interop / Linux (6.0)	2m 50s
Cxx interop / Cxx interop / Linux (nightly-next)	3m 26s
Cxx interop / Cxx interop / Linux (nightly-main)	3m 34s
Unit tests / Unit tests / Linux (5.9)	2m 29s
Unit tests / Unit tests / Linux (5.10)	2m 23s
Unit tests / Unit tests / Linux (6.0)	2m 51s
Unit tests / Unit tests / Linux (nightly-next)	3m 19s
Unit tests / Unit tests / Linux (nightly-main)	3m 18s
	41m 2s

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