TST: assert photometric error is numerically close to the analytic value

[rrjbca]

Description

The compatibility workflow is currently failing, see HERE

The development version of numpy appears to cause a small numerical change in the calculation of the Rykoff photometric error. This causes the unit test to fail because it asserts that the calculated error is exactly equal to the analytic value. This PR changes the test to assert that the calculated error is numerically close to the analytic value.

Compatibility tests are shown to work with this fix HERE

Checklist

• [x] Follow the Contributor Guidelines
• [ ] Write unit tests
• [ ] Write documentation strings
• [ ] Assign someone from your working team to review this pull request
• [x] Assign someone from the infrastructure team to review this pull request