build(deps): update rcgen requirement from 0.11.3 to 0.12.0 #1269

Job	Run time
Clippy	28s
Format	19s
Cargo Deny	21s
Check for documentation errors (stable)	26s
Check for documentation errors (beta)	26s
Validate external types appearing in public API	1m 2s
Check for documentation errors (nightly)	29s
Check cross compilation targets	43s
MSRV	1m 39s
Cargo Package	28s
Check semver compatibility	28s
Build+test (--all-features, stable)	46s
Build+test (stable, ubuntu-20.04)	35s
Measure coverage	39s
Build+test (--features=alloc, stable, ubuntu-20.04)	31s
Feature Powerset	35s
Build+test (--no-default-features, stable, ubuntu-20.04)	21s
Build+test (--no-default-features --features alloc,std, stable, ubuntu-20.04)	23s
Build+test (--all-features, --release, stable, ubuntu-20.04)	1m 26s
Verify that no-std modes do not rely on libstd (--no-default-features)	11s
Build+test (--all-features, nightly, ubuntu-20.04)	39s
Verify that no-std modes do not rely on libstd (--no-default-features --features alloc)	12s
Build+test (--all-features, beta, ubuntu-20.04)	46s
Build+test (--no-default-features --features alloc,std,aws_lc_rs, stable, macos-latest)	2m 36s
Build+test (--no-default-features --features alloc,std,aws_lc_rs, stable, windows-latest)	3m 40s
Build+test (--no-default-features --features alloc,std,aws_lc_rs, stable, ubuntu-latest)	42s
	20m 51s

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