Bump sql_database_instance create timeout from 30 to 40 minutes

[roaks3]

Related to hashicorp/terraform-provider-google#12912

The sql_database_instance tests that run nightly will frequently fail when they hit the 30 minute timeout. It is potentially more likely for configurations that involve clones and backups, but in any case, if the resource can realistically take >30 minutes to create, then the timeout should be higher, so it is only triggered when something is wrong.

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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.
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• Read the Release Notes Guide before writing my release note below.

Release Note Template for Downstream PRs (will be copied)

sql: changed the default create timeout of `google_sql_database_instance` to 40m from 30m

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

[modular-magician]

Tests analytics

Total tests: 2405
Passed tests 2153
Skipped tests: 251
Failed tests: 1

Action taken

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

TestAccRegionInstanceGroupManager_stateful

[modular-magician]

Tests failed during RECORDING mode:
TestAccRegionInstanceGroupManager_stateful[Error message] [Debug log]

Please fix these to complete your PR
View the build log or the debug log for each test

[trodge]

LGTM, adding Zhenhua for a second review.

[zli82016]

LGTM