minor bug fix utils.retrieve_over_http

[stellaprins]

Description

What is this PR

• Bug fix
• Addition of a new feature
• Other

Why is this PR needed?
While adding a test for utils.retrieve_over_http (see add test_atlas_repr_from_name) I noticed that when there is a connection error and no file in the specified output_file_path exists, the block of code below errors at output_file_path.unlink(), throwing an FileNotFoundError, instead of raising the ConnectionError (which is I think what is desired in this case).

    except requests.exceptions.ConnectionError:
        output_file_path.unlink()
        raise requests.exceptions.ConnectionError(
            f"Could not download file from {url}"
        )

What does this PR do?
sets output_file_path.unlink(missing_ok=True) so that the correct error message is shown in case of an ConnectionError.

References

#518

How has this PR been tested?

Added test_retrieve_over_http_ConnectionError to test_utils.py with XFAIL marker that can be removed after this PR is merged.

Is this a breaking change?

No.

Does this PR require an update to the documentation?

No.

Checklist:

• The code has been tested locally
• Tests have been added to cover all new functionality (unit & integration)
• The documentation has been updated to reflect any changes
• The code has been formatted with pre-commit

[stellaprins]

Failing codecov/patch can be ignored. PR #518 deals with test coverage.