gss-api: change `NegHints::hint_name` to GeneralStringRef type #2519

Job	Run time
build (1.85.0, thumbv7em-none-eabi)	1m 52s
build (1.85.0, wasm32-unknown-unknown)	1m 48s
build (stable, wasm32-unknown-unknown)	1m 34s
test (stable)	7m 27s
build (stable, thumbv7em-none-eabi)	1m 52s
test (1.85.0)	7m 27s
fuzz	2m 11s
minimal-versions	-6s
	24m 5s

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