Bump sphinx from 4.0.2 to 4.0.3 in /docs

[dependabot-preview]

Bumps sphinx from 4.0.2 to 4.0.3.

Changelog

Sourced from sphinx's changelog.

Release 4.0.3 (released Jul 05, 2021)

Features added

• C, add C23 keywords _Decimal32, _Decimal64, and _Decimal128.
• #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: changeset domain: :rst:dir:versionchanged with contents being a list will cause error during pdf build
• #9313: LaTeX: complex table with merged cells broken since 4.0
• #9305: LaTeX: backslash may cause Improper discretionary list pdf build error with Japanese engines
• #9354: C, remove special macro names from the keyword list. See also :confval:c_extra_keywords.
• #9322: KeyError is raised on PropagateDescDomain transform

Commits

• 007795d Bump to 4.0.3 final
• 779d902 Merge pull request #9326 from tk0miya/rebirth_of_force_decode
• a1994ac Merge branch '4.0.x' into rebirth_of_force_decode
• 723ad78 Merge pull request #9334 from tk0miya/9322_KeyError_from_PropageteDescDomain
• 072cdf2 Merge branch '4.0.x' into 9322_KeyError_from_PropageteDescDomain
• df5764d Merge pull request #9356 from jakobandersen/c_extra_keywords
• 50f5280 C, keyword changes
• 8939a75 Merge pull request #9335 from jfbu/9305_platex_backslash_upquote
• ef9b55c Fix #9305 LaTeX: backslash in sphinxupquote error with Japanese
• 7673cd6 Merge pull request #9333 from tk0miya/9330_versionchanged_breaks_list
• Additional commits viewable in compare view

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