Update mariadb Docker tag to v20.3.1

This MR contains the following updates:

Package	Type	Update	Change
mariadb (source)	HelmChart	minor	20.2.4 -> 20.3.1

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Release Notes

bitnami/charts (mariadb)

v20.3.1

• [bitnami/mariadb] Release 20.3.1 (#​32014)

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