mirgen: improve scope-only `block` support #4102

Job	Run time
Provide additional context for the workflow	6s
Build release binaries (Linux)	12m 10s
Build release binaries (macOS)	10m 59s
Build source archive	4m 16s
Test the compiler and stdlib (Linux, batch #0)	9m 4s
Build and test tooling (Linux)	5m 29s
Test the compiler and stdlib (Linux, batch #1)	11m 44s
Build docs and release artifacts (Linux)	10m 51s
Build and test tooling (macOS)	6m 10s
Test the compiler and stdlib (macOS, batch #0)	9m 39s
Build docs and release artifacts (macOS)	10m 56s
Test the compiler and stdlib (macOS, batch #1)	9m 48s
Build release artifacts from source archive (Linux)	14m 58s
Build release artifacts from source archive (macOS)	12m 41s
Test release artifacts	3m 10s
All check passed	1s
	2h 12m 2s

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