Set GOOGLE_TPU_V2_VM_RUNTIME_VERSION for VCR tests

[zli82016]

Part of hashicorp/terraform-provider-google#16957

A couple of tpu v2 vm tests failed with the capacity error.

Error: Error waiting to create Vm: Error waiting for Creating Vm: Error code 8, message: There is no more capacity in the zone "us-central1-c"

To fix the issue, the service team suggested to use a test vm runtime version. But this runtime version is only for testing and should not be exposed to public. https://buganizer.corp.google.com/issues/306250637#comment10

So an environment variable is used to store the value.

I created a secret for this environment variable and set it up for VCR tests in this PR.

Release Note Template for Downstream PRs (will be copied)

[zli82016]

/gcbrun

[zli82016]

/gcbrun

[zli82016]

/gcbrun

[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 ( 2 files changed, 11 insertions(+), 10 deletions(-))
Terraform Beta: Diff ( 4 files changed, 22 insertions(+), 17 deletions(-))

[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 ( 2 files changed, 11 insertions(+), 10 deletions(-))
Terraform Beta: Diff ( 4 files changed, 23 insertions(+), 17 deletions(-))

[modular-magician]

Tests analytics

Total tests: 3335
Passed tests 2996
Skipped tests: 338
Affected tests: 1

Click here to see the affected service packages

all service packages are affected

Action taken

Found 1 affected test(s) by replaying old test recordings. Starting RECORDING based on the most recent commit. Click here to see the affected tests

TestAccComputeRegionPerInstanceConfig_removeInstanceOnDestroy

Get to know how VCR tests work

[modular-magician]

$\textcolor{green}{\textsf{Tests passed during RECORDING mode:}}$
TestAccComputeRegionPerInstanceConfig_removeInstanceOnDestroy[Debug log]

Rerun these tests in REPLAYING mode to catch issues

$\textcolor{green}{\textsf{No issues found for passed tests after REPLAYING rerun.}}$

---

$\textcolor{red}{\textsf{Errors occurred during RECORDING mode. Please fix them to complete your PR.}}$
View the build log or the debug log for each test

[modular-magician]

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

Diff report

Your PR hasn't generated any diffs, but I'll let you know if a future commit does.