Fix Test Runs test suite

[aaabdelgany]

Description

This PR fixes the test suite for test runs by enabling tests via the TestConfig object.

External links

https://developer.hashicorp.com/terraform/cloud-docs/api-docs/private-registry/modules#update-a-private-registry-module

Output from tests

go test -run TestTestRun -v
=== RUN   TestTestRunsList
=== RUN   TestTestRunsList/without_list_options
=== RUN   TestTestRunsList/empty_list_options
=== RUN   TestTestRunsList/with_page_size
--- PASS: TestTestRunsList (12.42s)
    --- PASS: TestTestRunsList/without_list_options (0.34s)
    --- PASS: TestTestRunsList/empty_list_options (0.60s)
    --- PASS: TestTestRunsList/with_page_size (0.22s)
=== RUN   TestTestRunsRead
=== RUN   TestTestRunsRead/when_the_test_run_exists
=== RUN   TestTestRunsRead/when_the_test_run_does_not_exist
--- PASS: TestTestRunsRead (6.34s)
    --- PASS: TestTestRunsRead/when_the_test_run_exists (0.22s)
    --- PASS: TestTestRunsRead/when_the_test_run_does_not_exist (0.30s)
=== RUN   TestTestRunsCreate
=== RUN   TestTestRunsCreate/with_a_configuration_version
=== RUN   TestTestRunsCreate/without_a_configuration_version
=== RUN   TestTestRunsCreate/without_a_module
=== RUN   TestTestRunsCreate/without_an_organisation
--- PASS: TestTestRunsCreate (6.35s)
    --- PASS: TestTestRunsCreate/with_a_configuration_version (0.34s)
    --- PASS: TestTestRunsCreate/without_a_configuration_version (0.00s)
    --- PASS: TestTestRunsCreate/without_a_module (0.00s)
    --- PASS: TestTestRunsCreate/without_an_organisation (0.00s)
=== RUN   TestTestRunsLogs
=== RUN   TestTestRunsLogs/when_the_log_exists
=== RUN   TestTestRunsLogs/when_the_log_does_not_exist
--- PASS: TestTestRunsLogs (28.55s)
    --- PASS: TestTestRunsLogs/when_the_log_exists (22.74s)
    --- PASS: TestTestRunsLogs/when_the_log_does_not_exist (0.17s)
=== RUN   TestTestRunsCancel
=== RUN   TestTestRunsCancel/when_the_run_exists
=== RUN   TestTestRunsCancel/when_the_run_does_not_exist
--- PASS: TestTestRunsCancel (6.04s)
    --- PASS: TestTestRunsCancel/when_the_run_exists (0.24s)
    --- PASS: TestTestRunsCancel/when_the_run_does_not_exist (0.29s)
PASS
ok  	github.com/hashicorp/go-tfe	59.888s

[brandonc]

If you don't mind removing; I don't think I see a need for release notes about unit test additions 🙃

[aaabdelgany]

8002d94

[github-actions]

Reminder to the contributor that merged this PR: if your changes have added important functionality or fixed a relevant bug, open a follow-up PR to update CHANGELOG.md with a note on your changes.