BLD: Set scipy oldest supported version to 1.6

[rrjbca]

Description

In scipy 1.14 the scipy.integrate.cumtrapz will be deprecated. However the alias scipy.integrate.cumulative_trapezoid was not added until scipy 1.6. This pull request increases the oldest supported version of scipy to 1.6.

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