I want HEREDOC support too (in Debian sid / experimental environment),
but it is removed since buildah 1.33.1+ds1-1...
Quoted from changelog.Debian.gz:
```
golang-github-containers-buildah (1.33.1+ds1-1) experimental; urgency=medium
* New upstream release
* Revert heredoc and --checksum support in Dockerfiles to workaround ancient
docker.io package in Debian, cf #1051202
```
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-- Name: SATOH Fumiyasu @ OSSTech Corp., Japan (fumiyas @ osstech co jp)
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