remove dependency upper bounds in pyproject.toml

[spherical-tensor]

The package pyproject toml is using ^ limit some packages which is causing versioning conflicts.
^ in poetry prevents changes on the leftmost non-zero digit. In the case of, for example, pampy = "^0.2.1", we're stuck with the minor revision 0.2.x and only have wiggle room to change the patch versions; which is problematic.
Setting some packages to >= could be useful.