Migrate resource compute instance group manager test to use transport_tpg

[jcromanu]

…_tpg

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compute: migrated `google_compute_instance_group_manager` resource  to use direct HTTP rather than a client library

[github-actions]

Googlers: For automatic test runs see go/terraform-auto-test-runs.

@roaks3, a repository maintainer, has been assigned to review your changes. If you have not received review feedback within 2 business days, please leave a comment on this PR asking them to take a look.

You can help make sure that review is quick by doing a self-review and by running impacted tests locally.

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes for commit 5fff8cf:

Diff report

Your PR generated the following diffs in downstream repositories:

Repository	Diff Link	Changes
google provider	View Diff	1 file changed, 10 insertions(+), 2 deletions(-)
google-beta provider	View Diff	1 file changed, 10 insertions(+), 2 deletions(-)

Test report

Analytics

Total Tests	Passed	Skipped	Affected
1422	1331	91	0

Affected Service Packages

• compute

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Step 1: Replaying Mode

🟢 All tests passed in Replaying mode! No Recording was needed.

View the build log

@jcromanu, @roaks3, @pjotrekk VCR tests complete for 5fff8cf!

[github-actions]

@roaks3 This PR has been waiting for review for 3 weekdays. Please take a look! Use the label disable-review-reminders to disable these notifications.

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes for commit 5125d4b:

Diff report

Your PR generated the following diffs in downstream repositories:

Repository	Diff Link	Changes
google provider	View Diff	1 file changed, 10 insertions(+), 2 deletions(-)
google-beta provider	View Diff	1 file changed, 10 insertions(+), 2 deletions(-)

Test report

Analytics

Total Tests	Passed	Skipped	Affected
1427	1336	91	0

Affected Service Packages

• compute

Learn how VCR tests work

---

Step 1: Replaying Mode

🟢 All tests passed in Replaying mode! No Recording was needed.

View the build log

@jcromanu, @roaks3, @pjotrekk, @WentaoNi VCR tests complete for 5125d4b!