X509_dup.pod: add caveat that extra data is not copied and hints, e.g… #1573

Job	Run time
cygwin (windows-2019, win64, -DCMAKE_C_COMPILER=gcc --strict-warnings no-fips)	31m 8s
plain (windows-2019)	15m 59s
shared (windows-2019, win64, enable-fips)	28m 8s
minimal (windows-2019)	9m 59s
plain (windows-2022)	16m 31s
shared (windows-2019, win32, --strict-warnings no-fips)	30m 13s
minimal (windows-2022)	8m 20s
shared (windows-2022, win64, enable-fips)	27m 40s
shared (windows-2022, win32, --strict-warnings no-fips)	31m 20s
	3h 19m 18s

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