Add `symtable` to the list of modules with a CLI

[picnixz]

Documenting the symtable CLI was first not considered since it previously included self-tests. This is no more the case and the module now features a full-fledged CLI (only since 3.13).

As such, I suggest adding it to the list of modules documented in cmdline.rst.

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• Related: gh-85098: Implement functional CLI of symtable #109112
• Specialization of: Add a page to the documentation listing stdlib modules with a command-line interface (CLI) #109435

Linked PRs

• gh-123834: Add symtable to the list of modules with a CLI #123835
• [3.13] gh-123834: Add symtable to the list of modules with a CLI (GH-123835) #123862

[vstinner]

Merged, thanks.