Fix stale --help text on keys address name argument.

Author: fnando

FULL_HELP_DOCS.md

@@ -1154,7 +1154,7 @@ Given an identity return its address (public key)
 
 ###### **Arguments:**
 
-- `<NAME>` — Name of identity to lookup, default test identity used if not provided
+- `<NAME>` — Name of identity to lookup. Required unless `--ledger` is provided
 
 ###### **Options:**
 

cmd/soroban-cli/src/commands/keys/public_key.rs

@@ -43,7 +43,7 @@ impl Args {
 #[derive(Debug, clap::Parser, Clone)]
 #[group(skip)]
 pub struct Cmd {
-    /// Name of identity to lookup, default test identity used if not provided
+    /// Name of identity to lookup. Required unless `--ledger` is provided.
     #[arg(required_unless_present = "ledger")]
     pub name: Option<UnresolvedMuxedAccount>,