* gnu/packages/astronomy.scm (python-reproject): Enable tests.
[arguments]: <#:tests-flags>: Add them as seen in tox.ini.
<#:phases>: Rename 'writable-home to 'prepare-test-environment to reflect
purpose and build extension before tests.
[native-inputs]: Add python-xdist.
Change-Id: I7a5454e3ce241b7a54626f8aba27602b4965c25b
03776790b7