Update renovate/renovate Docker tag to v31.21.0

This MR contains the following updates:

Package	Type	Update	Change
renovate/renovate	Kustomization	minor	31.19.0 -> 31.21.0

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Release Notes

renovatebot/renovate

v31.21.0

Features

• Add 'and', 'or' and 'containsString' to handlebar helpers (#​13341) (7770888)

v31.20.0

Features

• datasource/pypi: override mkdocs-material source url (#​13376) (8aadfbc)

v31.19.1

31.19.1 (2022-01-06)

Bug Fixes

• manager/pip_requirements: handle lines with environment markers in requirements.txt (#​13403) (3972609)

Miscellaneous Chores

• deps: update dependency conventional-changelog-conventionalcommits to v4.6.3 (#​13391) (2fa5113)
• preview presets: improve descriptions (#​13392) (c84748e)

Code Refactoring

• More strict null checks (#​13387) (9743f1e)
• ruby: ensure strict null check (#​13278) (0331116)

Documentation

• capitalize proper nouns (#​13379) (da7092e)
• fix preset layout (#​13377) (6d5f4a5)
• package presets: capitalize proper nouns (#​13402) (b4470ea)
• running renovate: update redirected links (#​13381) (65229c8)
• update redirected links (#​13380) (1fd2973)

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