Fix vault cli errors on 'encrypt_string_read_stdin' (#21675)

'encrypt_string' only options were being referenced when using
other vault subcommands. That code is moved inside a check
for 'encrypt_string' action now.

lib/ansible/cli/vault.py

@@ -109,6 +109,7 @@ class VaultCLI(CLI):
             if self.options.output_file and len(self.args) > 1:
                 raise AnsibleOptionsError("At most one input file may be used with the --output option")
 
+        if self.action == 'encrypt_string':
             if '-' in self.args or len(self.args) == 0 or self.options.encrypt_string_stdin_name:
                 self.encrypt_string_read_stdin = True