Node_config image_type case diff suppress

[slevenick]

Fixes: hashicorp/terraform-provider-google#7336

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• 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).
• Generated Terraform, and ran make test and make lint to ensure it passes unit and linter tests.
• 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).
• Ran relevant acceptance tests (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)

container: fixed `node_config.image_type` perma-diff when specified in lower case.

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 2 files changed, 5 insertions(+), 4 deletions(-))
Terraform Beta: Diff ( 2 files changed, 5 insertions(+), 4 deletions(-))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=149268"

[slevenick]

/gcbrun

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 2 files changed, 5 insertions(+), 4 deletions(-))
Terraform Beta: Diff ( 2 files changed, 5 insertions(+), 4 deletions(-))

[modular-magician]

I have triggered VCR tests based on this PR's diffs. See the results here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=149640"

[modular-magician]

I have triggered VCR tests in RECORDING mode for the following tests that failed during VCR: TestAccProviderMeta_setModuleName|TestAccComputeSnapshot_encryptionCMEK|TestAccContainerCluster_withSandboxConfig|TestAccContainerNodePool_withSandboxConfig|TestAccMonitoringDashboard_basic|TestAccMonitoringDashboard_gridLayout|TestAccMonitoringDashboard_rowLayout|TestAccMonitoringDashboard_update You can view the result here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=149722"