ci: run only external deps tests (#96) #799

Job	Run time
Build & test (stable, ubuntu-latest)	1m 45s
Build & test (stable, macos-latest)	1m 43s
Build & test (stable, windows-latest)	5m 23s
Build & test (nightly, ubuntu-latest)	4m 34s
Build & test (nightly, macos-latest)	5m 4s
Build & test (nightly, windows-latest)	8m 58s
Test coverage checks	3m 45s
Build with each feature combination	2m 30s
Clippy lint checks	22s
Test with external dependencies	3m 1s
Minimal dependency versions build	1m 16s
Machete dependencies checks	15s
Miri test	8m 31s
Code formatting checks	17s
	47m 24s

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