bump write-fonts to 0.21.1 #1906

Job	Run time
cargo check no std	1m 13s
cargo check no std	1m 23s
Rustfmt	40s
Rustfmt	38s
Build GS and check the result	2m 45s
Build GS and check the result	2m 41s
resources/scripts/ots_test.sh	57s
resources/scripts/ots_test.sh	1m 2s
Clippy lints	38s
Clippy lints	40s
cargo test fea-rs	55s
cargo test fea-rs	57s
fontbe tests	46s
fontbe tests	42s
fontc tests	1m 14s
fontc tests	1m 6s
tests other than fontbe,fontc	1m 51s
tests other than fontbe,fontc	1m 56s
	22m 4s

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