harden falcon key handling #5279

Job	Run time
make check (--disable-oldtls --disable-tls13 --enable-psk -disable-rsa --disable-dh -disable-ecc ...	32s
make check (--enable-psk --disable-mlkem C_EXTRA_FLAGS=-DWOLFSSL_STATIC_PSK --disable-rsa --disa...	39s
make check (--enable-psk --disable-mlkem C_EXTRA_FLAGS="-DWOLFSSL_STATIC_PSK -DWOLFSSL_OLDTLS_SH...	57s
make check (--disable-oldtls --disable-tlsv12 --enable-tls13 --enable-psk -disable-rsa --disable-...	36s
make check (--enable-psk --enable-cert-with-extern-psk --disable-mlkem)	53s
	3m 37s

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