deps: Update gcr.io/cloud-sql-connectors/cloud-sql-proxy Docker tag to v2.21.0

[renovate-bot]

This PR contains the following updates:

Package	Update	Change
gcr.io/cloud-sql-connectors/cloud-sql-proxy	minor	2.19.0 → 2.21.0

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Release Notes

GoogleCloudPlatform/cloud-sql-proxy (gcr.io/cloud-sql-connectors/cloud-sql-proxy)

v2.21.0

Compare Source

Bug Fixes

• Update deprecated proxy options and update all dependencies (#​2531) (d9ae096)

Miscellaneous Chores

• release 2.21.0 (#​2533) (d813423)

v2.20.0

Compare Source

Features

• Add shutdown command to call the /quitquitquit endpoint. (#​2514) (f6747f9), closes #​2511

Bug Fixes

• Update dependency versions. (#​2520) (119dc23)

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