Housekeeping: update sdk, jamf client, terraform / unit test gh workflow

[w0de]

This contains those changes from #21 which do propose questionable and/or breaking changes to the API (ie, no change to jamf_staticComputerGroup.computer.{serial_number,id}, plus some overdue dependency updates.

What's included:

• Updates the go-jamf-api dependency to the latest version v0.0.0-20231020015325-f3a01d49ab57
• Updates the terraform version used for tests to 1.6.5
• Updates terraform-plugin-sdk to 2.16.0
• Amends OAuth support to use go-jamf-api's WithOAuth option.
• Amends func testAccPreCheck to require either OAuth or basic credentials, not both.
• Adds a unit test workflow. (All tests are currently acc tests and so this will always pass if lint passes. For future use.)

Note that acceptance tests are still not passing. Rather than smush partial fixes into this delta, I've opened issues (#24, #25) and will tackle them in discrete PRs.