Update dependency Sphinx to v4.0.3

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
Sphinx (source)	==4.0.2 -> ==4.0.3

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Release Notes

sphinx-doc/sphinx

### [`v4.0.3`](https://togithub.com/sphinx-doc/sphinx/blob/master/CHANGES#Release-403-released-Jul-05-2021) [Compare Source](https://togithub.com/sphinx-doc/sphinx/compare/v4.0.2...v4.0.3) \===================================== ## Features added - C, add C23 keywords `_Decimal32`, `_Decimal64`, and `_Decimal128`. - [#​9354](https://togithub.com/sphinx-doc/sphinx/issues/9354): C, add :confval:`c_extra_keywords` to allow user-defined keywords during parsing. - Revert the removal of `sphinx.util:force_decode()` to become some 3rd party extensions available again during 5.0 ## Bugs fixed - [#​9330](https://togithub.com/sphinx-doc/sphinx/issues/9330): changeset domain: :rst:dir:`versionchanged` with contents being a list will cause error during pdf build - [#​9313](https://togithub.com/sphinx-doc/sphinx/issues/9313): LaTeX: complex table with merged cells broken since 4.0 - [#​9305](https://togithub.com/sphinx-doc/sphinx/issues/9305): LaTeX: backslash may cause Improper discretionary list pdf build error with Japanese engines - [#​9354](https://togithub.com/sphinx-doc/sphinx/issues/9354): C, remove special macro names from the keyword list. See also :confval:`c_extra_keywords`. - [#​9322](https://togithub.com/sphinx-doc/sphinx/issues/9322): KeyError is raised on PropagateDescDomain transform

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[coveralls]

Coverage remained the same at 88.829% when pulling 1f389f99cd79612509979cd0de59ddcbaddc4658 on renovate/sphinx-4.x into fb518e6eaf0cd78eeeaeca327302f260aeda9147 on develop.