Quarantine Microsoft.AspNetCore.Identity.Test.UserManagerTest

The `UserManagerTest` class in `src/Identity/test/Identity.Test/UserManagerTest.cs` is intermittently failing due to a metrics timing flakiness issue. Multiple test methods fail with `Assert.Collection() Failure: Item comparison failure` where the measured duration of an Identity operation is reported as `0`, violating the assertion `Duration should be greater than 0.` in the metrics helper.

All failures share the same root cause: a metrics instrument records a duration of `0` for a store operation, likely when the operation completes too quickly for the timer resolution on the test machine.

## Failing methods

The following 14 test methods have been observed failing across 2 CI builds:

- `PasswordMethodsFailWhenStoreNotImplemented`
- `UsersEmailMethodsFailWhenStoreNotImplemented`
- `CheckPasswordWillRehashPasswordWhenNeeded`
- `DeleteCallsStore_Failure`
- `ClaimMethodsFailWhenStoreNotImplemented`
- `UpdateFailsWithNullSecurityStamp`
- `CreateFailsWithNullSecurityStamp`
- `DeleteCallsStore_Success`
- `UsersPhoneNumberMethodsFailWhenStoreNotImplemented`
- `RemoveClaimCallsStore`
- `LoginMethodsFailWhenStoreNotImplemented`
- `RemoveClaimsCallsStore`
- `UpdateClaimCallsStore`
- `SecurityStampMethodsFailWhenStoreNotImplemented`

## Error

```
Assert.Collection() Failure: Item comparison failure
↓ (pos 0)
Collection: [CollectedMeasurement`1 { Tags = [["aspnetcore.identity.user_type"] = "Microsoft.AspNetCore.Identity.Test.PocoUser", ...], Value = 0 }]
Error: Duration should be greater than 0.
```

## CI build links

- https://dev.azure.com/dnceng-public/public/_build/results?buildId=1488387 (2026-06-30, `batch_3--net11.0`)
- https://dev.azure.com/dnceng-public/public/_build/results?buildId=1458137 (2026-06-10, `batch_3--net11.0`)

> Generated by [Daily Test Quarantine Management](https://github.com/dotnet/aspnetcore/actions/runs/28513280759) · 862.7 AIC · ⌖ 9.22 AIC · ⊞ 2.9K · [◷](https://github.com/search?q=repo%3Adotnet%2Faspnetcore+is%3Aissue+%22gh-aw-workflow-call-id%3A+dotnet%2Faspnetcore%2Ftest-quarantine%22&type=issues)

Start in src/Identity/test/Identity.Test/UserManagerTest.cs and review the listed failing methods together with the metrics helper assertion that rejects a duration of 0. Use the two linked CI builds as failure context and verify the affected tests no longer produce zero-duration measurements or intermittent collection failures; the issue does not specify the quarantine mechanism or exact code change.

Written by the indexing model from the issue text.