Bump build base version to v1.21.9b1

[github-actions]

Update build base version

Bump to latest build base version in Dockerfile

changed lines [2] of file "/tmp/updatecli/github/rancher/image-build-multus/Dockerfile"

v1.21.9b1

Release published on the 2024-04-04 17:08:31 +0000 UTC at the url https://github.com/rancher/image-build-base/releases/tag/v1.21.9b1

Bump to latest build base version in Dockerfile

1 file(s) updated with " image: rancher/hardened-build-base:v1.21.9b1": * .drone.yml

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