Add sanity checks in key export #4051

Job	Run time
build library (--enable-intelasm --enable-sp-asm --enable-experimental --enable-kyber=yes,origina...	33s
build library (--disable-asm)	36s
build library (--enable-intelasm --enable-sp-asm)	31s
build library (--enable-intelasm --enable-sp-asm --enable-all-crypto --enable-experimental --enab...	58s
build library (--disable-asm --enable-all-crypto --enable-experimental --enable-kyber=yes,origina...	57s
build library (--disable-asm --enable-experimental --enable-kyber=yes,original --enable-lms --ena...	34s
	4m 9s

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