fix: guard wc_Ed448PublicKeyToDer ed448_export_public call for FIPS<7 #2481

Job	Run time
make check (--enable-sm2 --enable-sm3 --enable-sm4-ecb --enable-sm4-cbc --enable-sm4-ctr --enable...	57s
make check (--enable-all --enable-sm2 --enable-sm3 --enable-sm4-ecb --enable-sm4-cbc --enable-sm4...	3m 1s
make check (--enable-sm2 --enable-sm3 --enable-sm4-gcm --enable-sm4-ccm --enable-sha3)	54s
	4m 52s

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