Update validator-amp-mega-menu.protoascii

[ilknureren]

Currently, the documentation only provides one example of "Disallowed tag ancestor" error:

Currently, the only example is a template tag, which may not be nested under another template tag.

However, it seems that the svg tag cannot be nested under amp-mega-menu either.
Could it be added?

If not, we should document that "The tag 'svg' may not appear as a descendant of tag 'amp-mega-menu'."

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[amp-owners-bot]

Hey @ampproject/wg-caching, these files were changed:

• extensions/amp-mega-menu/validator-amp-mega-menu.protoascii

[wassgha]

We added this for amp-nested-menu through #26463 so it makes sense to do it for amp-mega-menu :)

[ilknureren]

@googlebot I signed it!

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[twifkak]

Thanks for the change! Validator protoascii usage looks good, but I'll leave it to @wassgha or another mega-menu OWNER to approve.

[wassgha]

LGTM