Fix DataFusion instance versions used in tests

[roaks3]

fixes hashicorp/terraform-provider-google#11822

Per https://cloud.google.com/data-fusion/docs/support/version-support-policy, some of the versions we were using for these tests have been deprecated.

For the tests that do not explicitly deal with the version, I've removed it to prevent this from happening in the future. For the _update test, we do want to test upgrading the version, so I've chosen the latest version I could (6.7.0).

If this PR is for Terraform, I acknowledge that I have:

• Searched through the issue tracker for an open issue that this either resolves or contributes to, commented on it to claim it, and written "fixes {url}" or "part of {url}" in this PR description. If there were no relevant open issues, I opened one and commented that I would like to work on it (not necessary for very small changes).
• Ensured that all new fields I added that can be set by a user appear in at least one example (for generated resources) or third_party test (for handwritten resources or update tests).
• Generated Terraform providers, and ran make test and make lint in the generated providers to ensure it passes unit and linter tests.
• Ran relevant acceptance tests using my own Google Cloud project and credentials (If the acceptance tests do not yet pass or you are unable to run them, please let your reviewer know).
• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

Terraform GA: Diff ( 3 files changed, 3 insertions(+), 6 deletions(-))
Terraform Beta: Diff ( 3 files changed, 3 insertions(+), 6 deletions(-))
TF Validator: Diff ( 2 files changed, 3 insertions(+), 3 deletions(-))
TF OiCS: Diff ( 2 files changed, 2 deletions(-))

[modular-magician]

Tests analytics

Total tests: 2463
Passed tests 2204
Skipped tests: 255
Failed tests: 4

Action taken

Triggering VCR tests in RECORDING mode for the tests that failed during VCR. Click here to see the failed tests

TestAccFirebaserulesRelease_BasicRelease|TestAccDataFusionInstance_update|TestAccDataFusionInstance_dataFusionInstanceEventExample|TestAccDataFusionInstance_dataFusionInstanceFullExample

[modular-magician]

Tests passed during RECORDING mode:
TestAccFirebaserulesRelease_BasicRelease[Debug log]
TestAccDataFusionInstance_update[Debug log]
TestAccDataFusionInstance_dataFusionInstanceEventExample[Debug log]
TestAccDataFusionInstance_dataFusionInstanceFullExample[Debug log]

All tests passed
View the build log or the debug log for each test

[c2thorn]

nice plan for going forward!