Set region as optional in doc for cloud_scheduler_job

[edwardmedia]

Fixes hashicorp/terraform-provider-google#6975

Release Note Template for Downstream PRs (will be copied)

[modular-magician]

Hello! I am a robot who works on Magic Modules PRs.

I have detected that you are a community contributor, so your PR will be assigned to someone with a commit-bit on this repo for initial review.

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@slevenick, please review this PR or find an appropriate assignee.

[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, 11 insertions(+), 11 deletions(-))
Terraform Beta: Diff ( 2 files changed, 11 insertions(+), 11 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=138382"

[modular-magician]

I have triggered VCR tests in RECORDING mode for the following tests that failed during VCR: TestAccCloudBuildTrigger_cloudbuildTriggerBuildExample|TestAccCloudBuildTrigger_basic|TestAccComputeInstanceTemplate_shieldedVmConfig1|TestAccComputeInstanceTemplate_shieldedVmConfig2|TestAccComputeInstance_shieldedVmConfig1|TestAccComputeInstance_shieldedVmConfig2|TestAccContainerCluster_withReleaseChannelEnabled|TestAccContainerCluster_withReleaseChannelEnabledDefaultVersion|TestAccContainerCluster_misc|TestAccContainerCluster_withInvalidReleaseChannel|TestAccEndpointsService_basic|TestAccOSConfigPatchDeployment_osConfigPatchDeploymentFullExample|TestAccRedisInstance_redisInstanceFullExample|TestAccRedisInstance_redisInstancePrivateServiceExample|TestAccSqlDatabaseInstance_dontDeleteDefaultUserOnReplica|TestAccSqlDatabaseInstance_settings_basic|TestAccSqlDatabaseInstance_replica|TestAccSqlDatabaseInstance_slave|TestAccSqlDatabaseInstance_highAvailability|TestAccSqlDatabaseInstance_settingsDowngrade|TestAccSqlDatabaseInstance_PointInTimeRecoveryEnabled|TestAccSqlDatabaseInstance_settings_upgrade|TestAccSqlDatabaseInstance_authNets|TestAccSqlDatabaseInstance_basic_with_user_labels You can view the result here: "https://ci-oss.hashicorp.engineering/viewQueued.html?itemId=138383"