Incorrect help output for EXPLAIN

**Describe the problem**

```
root@127.0.0.1:26257/movr> \h EXPLAIN
Command: EXPLAIN
Description: show the logical plan of a query
Category: miscellaneous
Syntax:
EXPLAIN
EXPLAIN ([PLAN ,] )
EXPLAIN (DISTSQL)
EXPLAIN ANALYZE [(DISTSQL)]
EXPLAIN ANALYZE (PLAN )

Explainable statements:
SELECT, CREATE, DROP, ALTER, INSERT, UPSERT, UPDATE, DELETE,
SHOW, EXPLAIN

Plan options:
TYPES, VERBOSE, OPT

See also:
https://www.cockroachlabs.com/docs/v25.1/explain.html
```

**To Reproduce**

1. `crdb demo --insecure`
2. `\h EXPLAIN`

The correct output should be something like `EXPLAIN ANALYZE (PLAN, VERBOSE) SELECT` (note the missing comma in the above output).

Jira issue: CRDB-49390