doc: fix keyObject.symmetricSize to be keyObject.symmetricKeySize

PR-URL: #25670
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>

Author: panva

doc/api/crypto.md

@@ -1172,7 +1172,7 @@ encryption mechanism, PEM-level encryption is not supported when encrypting
 a PKCS#8 key. See [RFC 5208][] for PKCS#8 encryption and [RFC 1421][] for
 PKCS#1 and SEC1 encryption.
 
-### keyObject.symmetricSize
+### keyObject.symmetricKeySize
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