doc: update crypto.createSecretKey history

Passing strings to `crypto.createSecretKey` was not added until v15.0.0
(specifically with commit dae283d). The existing documentation implies
its availability in prior versions which may cause confusion.

PR-URL: #35874
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

doc/api/crypto.md

@@ -2147,8 +2147,9 @@ added: v11.6.0
 changes:
   - version: v15.0.0
     pr-url: https://github.com/nodejs/node/pull/35093
-    description: The key can also be an ArrayBuffer. The encoding argument was
-                 added. The key cannot contain more than 2 ** 32 - 1 bytes.
+    description: The key can also be an ArrayBuffer or string. The encoding
+                 argument was added. The key cannot contain more than
+                 2 ** 32 - 1 bytes.
 -->
 
 * `key` {string|ArrayBuffer|Buffer|TypedArray|DataView}