Explicitly add PyPI as default package source for poetry

Fix the following warning:

Warning: In a future version of Poetry, PyPI will be disabled
automatically if at least one custom primary source is configured.
In order to avoid a breaking change and make your pyproject.toml
forward compatible, add PyPI explicitly via 'poetry source add pypi'.
By the way, this has the advantage that you can set the priority of
PyPI as with any other source.

pyproject.toml

@@ -22,9 +22,14 @@ homepage = "https://galaxyproject.org/"
 repository = "https://github.com/galaxyproject/galaxy/"
 documentation = "https://docs.galaxyproject.org/"
 
+[[tool.poetry.source]]
+name = "PyPI"
+priority = "default"
+
 [[tool.poetry.source]]
 name = "galaxyproject"
 url = "https://wheels.galaxyproject.org/simple"
+priority = "primary"
 
 [tool.poetry.dependencies]
 a2wsgi = "*"