chore(macros/LearnSidebar): add "HTML forms in legacy browsers"

[kashyapkaki]

Summary

Fixes #9349

Problem

Learn/Forms/HTML_forms_in_legacy_browsers page is missing from the MDN Web Forms sidebar.

Solution

Added "HTML form in legacy browsers" under the "Advanced forms articles" sidebar subsection.

Screenshot

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How did you test this change?

Verified by running the code locally.

[caugner]

LGTM, but I defer to @wbamberg about whether this is the right position in the sidebar.

[caugner]

@kashyapkaki Oh, it looks like some of your commits aren't signed. Can you please have a look at this failing check and follow the instructions? 🙏

[kashyapkaki]

@kashyapkaki Oh, it looks like some of your commits aren't signed. Can you please have a look at this failing check and follow the instructions? 🙏

Thanks for tagging. Yes, I've signed and pushed the commit again. Thank you.

[kashyapkaki]

@kashyapkaki Oh, it looks like some of your commits aren't signed. Can you please have a look at this failing check and follow the instructions? 🙏

Thanks for tagging. Yes, I've signed and pushed the commit again. Thank you.

@caugner Is that still showing I haven't signed the commits?

[caugner]

Is that still showing I haven't signed the commits?

Unfortunately, yes. 🤔 Could you please try to follow these steps:

1. Make sure to not have any uncommitted changes; in doubt run git stash to be safe.
2. Run git checkout main and then git reset --hard 135c236 and finally git push --force

This should put the branch in a state where it has a single verified commit.