fix: Skip NavigableString in HTML parsing

[higuhigu-lb]

This PR skips NavigableString elements during HTML parsing to avoid unwanted error.

Issue resolved by this Pull Request:
Resolves #463

Checklist:

• Documentation has been updated, if necessary.
• Examples have been added, if necessary.
• Tests have been added, if necessary.

[mergify]

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🟢 Enforce conventional commit

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Make sure that we follow https://www.conventionalcommits.org/en/v1.0.0/

• title ~= ^(fix|feat|docs|style|refactor|perf|test|build|ci|chore|revert)(?:\(.+\))?(!)?:

[dolfim-ibm]

For reference, here is an example of NavigableString from the docs.

[dolfim-ibm]

@higuhigu-lb thanks for your first contribution. Please note that according to our contributing guidelines, we require sign-off commits.

You can update your PR with the following command

git rebase HEAD~1 --signoff

[higuhigu-lb]

@dolfim-ibm

Thank you for your helpful advice.
I have updated the commit accordingly.