testing in deployment workflow does not check for the correct version

[orbeckst]

The current deployment workflow tries to test the uploaded pypi (or testpypi) package by downloading the latest package, installing it, and running the test suite.

However, downloading "the latest package" can fail in multiple ways

1. The previous package is downloaded because pypi was not updated quickly enough. This may either lead to failures or false positives.
2. When testing with pre-release versions such as 1.1.0rc1, pip install GridDataFormats never considers pre-releases and always installs the latest stable so that we cannot properly test.

We can add a heuristic delay but that also addresses (1). A better approach would be to communicate the version number between workflow steps and then have pip install the exact version. Add either delay or retry functionality.