fix(airflow): Pin virtualenv

[adwk67]

Description

virtualenv 21.0.0 contains breaking changes.
From pypa/hatch#2193:

hatch will consume the latest version since it's anything equal or newer than 20.26.6.

This fix pins virtualenv with --with "virtualenv<21"

---

Tested build with 3.1.6:

...
 => => loading layer f6e3f5e59c53 65.54kB / 4.11MB                                                                                                                                                            2.7s
 => => loading layer ff863b32daad 6.93kB / 6.93kB                                                                                                                                                             2.6s
 => => loading layer 321a3a5efa32 69.63MB / 75.31MB                                                                                                                                                           2.5s
 => => loading layer 5f70bf18a086 32B / 32B                                                                                                                                                                   0.2s
Successfully built 1 image:
oci.stackable.tech/sdp/airflow:3.1.6-stackable0.0.0-dev

Definition of Done Checklist

Note

Not all of these items are applicable to all PRs, the author should update this template to only leave the boxes in that are relevant.

Please make sure all these things are done and tick the boxes

• Changes are OpenShift compatible
• All added packages (via microdnf or otherwise) have a comment on why they are added
• Things not downloaded from Red Hat repositories should be mirrored in the Stackable repository and downloaded from there
• All packages should have (if available) signatures/hashes verified
• Add an entry to the CHANGELOG.md file
• Integration tests ran successfully

TIP: Running integration tests with a new product image

The image can be built and uploaded to the kind cluster with the following commands:

boil build <IMAGE> --image-version <RELEASE_VERSION> --strip-architecture --load
kind load docker-image <MANIFEST_URI> --name=<name-of-your-test-cluster>

See the output of boil to retrieve the image manifest URI for <MANIFEST_URI>.

[NickLarsenNZ]

LGTM