docs/ssh: update algorithm_signer param after #9824 (#10126)

website/pages/api-docs/secret/ssh/index.mdx

@@ -211,10 +211,10 @@ This endpoint creates or updates a named role.
 - `allowed_user_key_lengths` `(map<string|int>: "")` – Specifies a map of ssh key types
   and their expected sizes which are allowed to be signed by the CA type.
 
-- `algorithm_signer` `(string: "ssh-rsa")` - Algorithm to sign keys with.  Valid
+- `algorithm_signer` `(string: "")` - Algorithm to sign keys with.  Valid
   values are `ssh-rsa`, `rsa-sha2-256`, and `rsa-sha2-512`.  Note that `ssh-rsa`
   is now considered insecure and is not supported by current OpenSSH versions.
-  Defaults to `ssh-rsa` for backwards compatibility.
+  If not specified, it will use the signer's default algorithm.
 
 ### Sample Payload