Travel tasks only accept == modifier

[DiTo97]

Generally, the definition of a Travel task has the following form:

tasks:
  <phase>:
    <step>:
      - task: <travel-task-package><modifier><version>
        name: <travel-task-name>
        config:
          .
          .
          .

where <travel-task-package> can either be a published package (e.g., on PyPI) or a local bag.

The problem is that, unless the optional arg python_module is provided, the only accepted <modifier> is ==, whereas all of them should be supported as in the function sanitize_versioned_package.

At the moment, a Travel task like the following crashes:

tasks:
  <phase>:
    <step>:
      - task: traveltask_google_artifact_registry~=0.0.1
        name: <travel-task-name>
        config:
          .
          .
          .

with the following error:

Traceback (most recent call last):
    ...
ModuleNotFoundError: No module named 'traveltask_google_artifact_registry~=0'

Implementing a fix should be quite easy since the file pip_sanitizers.py already has all the logic to check for different modifiers, and assert that any resulting split is a valid package.