Replace openwrt image

[eiskasten]

This PR tries to fix #4958 by replacing the openwrtorg/sdk with the openwrt/sdk docker image.

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  (added as entry in doc/news/_preparation_next_release.md which contains _(my name)_)
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  • add a line in doc/news/_preparation_next_release.md
  • reformat the code with scripts/dev/reformat-all
  • make all unit tests pass
  • fix all memleaks
  • fix the CI itself (or rebase if already fixed)
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Checklist

• I added unit tests for my code
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  (not in the PR description)
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[markus2330]

If this works, it would be perfect! 🚀

[eiskasten]

jenkins build libelektra please

[eiskasten]

jenkins build libelektra please

[eiskasten]

The jenkins pipeline ran through now, it is currently quite unstable and often fails due to java related tasks. However, the cirrus tasks which involve the scripts/docker/cirrus/arch/Dockerfile always fail. Cirrus reports: Container errored with 'ImagePullBackOff: Back-off pulling image "gcr.io/cirrus-ci-community/elektrainitiative/libelektra/scripts/docker/cirrus/arch/dockerfile:192f328646916150a6104131ce20859c"'. The base image of the dockerfile, archlinux:base-devel is available to my local docker instance.