update release notes and version for desispec/0.68.1 #5773

Job	Run time
Doc test (ubuntu-latest, 3.9)	48s
Test coverage (ubuntu-latest, 3.10, <6, <2, <1.23)	8m 4s
Test minimal env (ubuntu-latest, 3.10)	1m 4s
Style check (ubuntu-latest, 3.9)	22s
Unit tests (ubuntu-latest, 3.9, ==5.0, ==1.1.6, <1.23)	5m 59s
Unit tests (ubuntu-latest, 3.9, ==5.0, <2, <1.23)	5m 40s
API doc completeness test (ubuntu-latest, 3.9)	26s
Unit tests (ubuntu-latest, 3.9, <6, ==1.1.6, <1.23)	6m 4s
Unit tests (ubuntu-latest, 3.9, <6, <2, <1.23)	5m 39s
Unit tests (ubuntu-latest, 3.10, ==5.0, ==1.1.6, <1.23)	5m 58s
Unit tests (ubuntu-latest, 3.10, ==5.0, <2, <1.23)	5m 37s
Unit tests (ubuntu-latest, 3.10, <6, ==1.1.6, <1.23)	5m 51s
Unit tests (ubuntu-latest, 3.10, <6, <2, <1.23)	5m 41s
	57m 13s

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