Update generate matrix stript to use nightly_next #1368

Job	Run time
Construct integration test matrix	3s
Vsock tests	2m 57s
Unit tests / Construct unit test matrix	5s
Benchmarks / Construct Benchmarks matrix	3s
Cxx interop / Construct Cxx interop matrix	5s
Soundness / API breakage check	1m 57s
Soundness / Documentation check	2m 6s
Soundness / Broken symlinks check	4s
Soundness / Format check	45s
Soundness / License headers check	9s
Soundness / Python lint check	4s
Soundness / Shell check	38s
Soundness / Unacceptable language check	3s
Soundness / YAML lint check	4s
Integration tests / Linux (5.9)	17m 57s
Integration tests / Linux (5.10)	17m 56s
Integration tests / Linux (6.0)	17m 57s
Integration tests / Linux (nightly-6.1)	17m 57s
Integration tests / Linux (nightly-main)	17m 57s
Benchmarks / Benchmarks / Linux (5.9)	5m 19s
Benchmarks / Benchmarks / Linux (5.10)	4m 56s
Benchmarks / Benchmarks / Linux (6.0)	5m 41s
Benchmarks / Benchmarks / Linux (nightly-main)	4m 22s
Cxx interop / Cxx interop / Linux (5.9)	1m 10s
Cxx interop / Cxx interop / Linux (5.10)	1m 10s
Cxx interop / Cxx interop / Linux (6.0)	1m 27s
Cxx interop / Cxx interop / Linux (nightly-6.1)	1m 32s
Cxx interop / Cxx interop / Linux (nightly-main)	1m 38s
Unit tests / Unit tests / Linux (5.9)	3m 55s
Unit tests / Unit tests / Linux (5.10)	3m 56s
Unit tests / Unit tests / Linux (6.0)	4m 6s
Unit tests / Unit tests / Linux (nightly-6.1)	4m 37s
Unit tests / Unit tests / Linux (nightly-main)	4m 27s
	2h 27m 3s

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