[BUGFIX] Correct grid coordinates for ngrid=1

[gogannes]

[BUGFIX] Correct grid coordinates for ngrid=1

When ngrid=1 was chosen, np.linspace would just return the starting value of -1 * pt which would not place the point at the center of the rotor. With this fix the center of the rotor is chosen.

Related issue

1004

Impacted areas of the software

The generation of the y and z coordinates for each of the turbines is affected in cases where ngrid=1 is chosen.

Additional supporting information

See #1004

Test results, if applicable

Locally all existing tests run without issues. The example case of #1004 now works as expected.

[rafmudaf]

The CI infrastructure has gotten quite stale since v2. To address the failing tests, I suggest to remove macOS from the test matrix and stick with only Linux. In any case, this is consistent with what we've done in v3 and v4. You can make that change here: https://github.com/gogannes/floris/blob/v2/.github/workflows/continuous-integration-workflow.yaml#L28.

[misi9170]

The CI infrastructure has gotten quite stale since v2. To address the failing tests, I suggest to remove macOS from the test matrix and stick with only Linux. In any case, this is consistent with what we've done in v3 and v4. You can make that change here: https://github.com/gogannes/floris/blob/v2/.github/workflows/continuous-integration-workflow.yaml#L28.

Thanks @rafmudaf ---that sounds good. I'll create a separate PR that does that; and we can merge that first, then this one.

EDIT: The PR removing Mac OS tests is #1020