[Feature] Update documentation of integration tests as it relates to CircleCI / GHA

[dbeatty10]

Is this your first time submitting a feature request?

• I have read the expectations for open source contributors
• I have searched the existing issues, and I could not find an existing issue for this feature
• I am requesting a straightforward extension of existing dbt-spark functionality, rather than a Big Idea better suited to a discussion

Describe the feature

Update this documentation to reflect the switch from CircleCI to GitHub Actions in #923:

dbt-spark/.github/workflows/release.yml

Lines 89 to 94 in 2124423

	# The Spark repository uses CircleCI to run integration tests.
	# Because of this, the process of version bumps will be manual
	# which means that this stage will be used to audit the version
	# and changelog in sources.
	# We are passing `env_setup_script_path` as an empty string
	# so that the integration tests stage will be skipped.

Describe alternatives you've considered

No response

Who will this benefit?

Up-to-date documentation. I found this instance when doing a code search for "CircleCI".

Are you interested in contributing this feature?

No response

Anything else?

No response