SIA-R66 and SIA-R69 should (maybe) apply to submit buttons

[Jym77]

The visitor in nonDisabledText only return text nodes.
This does not include the text of some buttons which is provided by the value attribute or defaulting, e.g. <input type="submit" value="Next" /> has a text of Next and <input type="submit" /> has a text of (localised) Submit.

Since these are not text nodes, they are not inapplicable in the current state.
Note that the corresponding ACT rule is also only applicable to text nodes. See act-rules/act-rules.github.io#2204