Support older terraform versions in slices

[mwarkentin]

Steps to Reproduce

1. Touched some legacy terraform slices which use terraform 0.14.11: https://github.com/getsentry/ops/pull/9788

Expected Result

I expected that the GHA would use the version of terraform specified in .terraform-version within the slice.

Actual Result

│ Error: Unsupported Terraform Core version
│ 
│   on _init.tf line 2, in terraform:
│    2:   required_version = "= 0.14.11"
│ 
│ This configuration does not support Terraform version 1.5.3. To proceed,
│ either choose another supported Terraform version or update this version
│ constraint. Version constraints are normally set for good reason, so
│ updating the constraint may lead to other errors or unexpected behavior.