CreateImageIndexTests failing in CI

For now, OK to merge on failures.

[Pipelines - Run 20250615.12](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1068683&view=ms.vss-test-web.build-test-results-tab&runId=28918030&resultId=103893&paneView=dotnet-dnceng.dnceng-anon-build-release-tasks.helix-anon-test-information-tab)

StdErr:
```
Unable to find image 'registry:2' locally
docker: Error response from daemon: toomanyrequests: You have reached your unauthenticated pull rate limit. https://www.docker.com/increase-rate-limit.
See 'docker run --help'.
, but found 125 (difference of 125).
   at FluentAssertions.Execution.LateBoundTestFramework.Throw(String message)
   at FluentAssertions.Execution.DefaultAssertionStrategy.HandleFailure(String message)
   at FluentAssertions.Execution.AssertionScope.AddPreFormattedFailure(String formattedFailureMessage)
   at FluentAssertions.Execution.AssertionChain.FailWith(Func`1 getFailureReason)
   at FluentAssertions.Execution.AssertionChain.FailWith(Func`1 getFailureReason)
   at FluentAssertions.Execution.AssertionChain.FailWith(String message, Object[] args)
   at FluentAssertions.Numeric.NumericAssertionsBase`3.Be(T expected, String because, Object[] becauseArgs)
   at Microsoft.NET.TestFramework.Assertions.CommandResultAssertions.Pass() in /_/test/Microsoft.NET.TestFramework/Assertions/CommandResultAssertions.cs:line 27
   at Microsoft.NET.Build.Containers.IntegrationTests.DockerRegistryManager.StartAndPopulateDockerRegistry(ITestOutputHelper testOutput) in /_/test/Microsoft.NET.Build.Containers.IntegrationTests/DockerRegistryManager.cs:line 66
Spawn registry attempt #4 failed, Xunit.Sdk.XunitException: Expected value to be 0 because Expected command to pass but it did not.
File Name: docker
Arguments: run --rm --publish 5010:5000 --detach docker.io/library/registry:2
Exit Code: 125
```