Update rand_core requirement from 0.6 to 0.9 #1625

Job	Run time
setup	4s
extract-header-only-ml-kem	2m 57s
extract	2m 43s
extract-header-only-ml-dsa	3m 8s
diff-header-only-ml-kem	8s
build-header-only-ml-kem (macos-latest)	17s
build-header-only-ml-kem (ubuntu-latest)	32s
build-header-only-ml-kem (windows-latest)	1m 52s
diff	5s
build (macos-latest)	5m 30s
build (ubuntu-latest)	24m 1s
build (windows-latest)	3m 59s
build-header-only-ml-dsa (macos-latest)	17s
diff-header-only-ml-dsa	6s
build-header-only-ml-dsa (ubuntu-latest)	18s
build-header-only-ml-dsa (windows-latest)	1m 10s
report-status-tests	1s
report-status-all	1s
	47m 9s

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