CI failure in dotnet/runtime because of rate limiting in a devops NuGet feed

### Build

https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_build/results?buildId=1455317&view=logs&j=24dced49-d4a4-54d9-37f0-d60d0af2edf3

### Build leg reported

Build / osx-x64 Debug Libraries_CheckedCoreCLR / Build product

### Pull Request

https://github.com/dotnet/runtime/pull/129150

### Known issue core information

Fill out the known issue JSON section by following the [step by step documentation on how to create a known issue](https://github.com/dotnet/arcade/blob/main/Documentation/Projects/Build%20Analysis/KnownIssueJsonStepByStep.md#how-to-create-a-known-issue-step-by-step)

```json
{
"BuildRetry": false,
"ErrorMessage": [ "error NU1301: Unable to load the service index for source https://pkgs.dev.azure.com/dnceng/public/_packaging/", "Response status code does not indicate success: 500 (Internal Server Error - Request was blocked due to exceeding usage of resource 'Concurrency' in namespace 'IPAddress'." ],
"ExcludeConsoleLog": true
}
```

@dotnet/dnceng

### Release Note Category
- [ ] Feature changes/additions
- [ ] Bug fixes
- [ ] Internal Infrastructure Improvements
### Release Note Description

### Additional information about the issue reported

The error is:

> error NU1301: Unable to load the service index for source https:\//pkgs.dev.azure.com/dnceng/public/_packaging/darc-pub-dotnet-emsdk-b634e009/nuget/v3/index.json. Response status code does not indicate success: 500 (Internal Server Error - Request was blocked due to exceeding usage of resource 'Concurrency' in namespace 'IPAddress'. For more information on why your request was blocked, see the topic "Rate limits" on the Microsoft Web site (https:\//go.microsoft.com/fwlink/?LinkId=823950). (DevOps Activity ID: 06377538-A80D-4143-AAD2-DB5FE3BC424C)).

### Known issue validation
**Build: :mag_right:** https://dev.azure.com/dnceng-public/public/_build/results?buildId=1455317
**Error message validated:** `[error NU1301: Unable to load the service index for source https://pkgs\.dev\.azure\.com/dnceng/public/_packaging/[^/]+/nuget/v3/index\.json\. Response status code does not indicate success: 500 \(Internal Server Error - Request was blocked due to exceeding usage of resource 'Concurrency' in namespace 'IPAddress'\.`]
**Result validation:** :x: Known issue did not match with the provided build.
**Validation performed at:** 6/12/2026 9:14:46 AM UTC

### Report
#### Summary
|24-Hour Hit Count|7-Day Hit Count|1-Month Count|
|---|---|---|
|0|0|0|

### Known issue validation
**Build: :mag_right:** https://dev.azure.com/dnceng-public/public/_build/results?buildId=1455317
**Error message validated:** `[error NU1301: Unable to load the service index for source https://pkgs.dev.azure.com/dnceng/public/_packaging/ Response status code does not indicate success: 500 (Internal Server Error - Request was blocked due to exceeding usage of resource 'Concurrency' in namespace 'IPAddress'.`]
**Result validation:** :white_check_mark: Known issue matched with the provided build.
**Validation performed at:** 6/12/2026 3:24:57 PM UTC

### Report
#### Summary
|24-Hour Hit Count|7-Day Hit Count|1-Month Count|
|---|---|---|
|0|0|0|

### Report
|Build|Repository|Step Name|Console log|Pull Request|
|---|---|---|---|---|
|[1591668](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591668)|dotnet/runtime|Build product|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1591668/logs/626)|dotnet/runtime#133640|
|[1591270](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591270)|dotnet/runtime|Prepare TestHost with runtime Mono|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1591270/logs/2994)|dotnet/runtime#133364|
|[1591674](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591674)|dotnet/aspnetcore|Build SiteExtension|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1591674/logs/129)|dotnet/aspnetcore#69210|
|[1591266](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591266)|dotnet/runtime|Build product|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1591266/logs/1945)|dotnet/runtime#133366|
|[1591218](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591218)|dotnet/aspnetcore|Build SiteExtension|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1591218/logs/183)|dotnet/aspnetcore#69198|
|[1591290](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591290)|dotnet/runtime|Build product|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1591290/logs/155)||
|[1591171](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591171)|dotnet/machinelearning|Build Packages|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1591171/logs/404)|dotnet/machinelearning#7709|
|[1591150](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591150)|dotnet/maui|Run Integration Tests - Blazor |[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1591150/logs/1122)|dotnet/maui#38409|
|[1591137](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591137)|dotnet/maui|Run Integration Tests - Blazor windows|[Log](https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_apis/build/builds/1591137/logs/1122)||

|Build|Repository|Test|Pull Request|
|---|---|---|---|
|[1591815](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591815)|dotnet/aspnetcore|[Templates.Blazor.Test.BlazorWasmTemplateTest.BlazorWasmStandaloneTemplateCanCreateBuildPublish](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591815&view=ms.vss-test-web.build-test-results-tab&runId=43940374&resultId=123041)||
|[1591224](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591224)|dotnet/aspnetcore|[Templates.Mvc.Test.MvcTemplateTest.MvcTemplate_NoAuthNoHttpsFSharp](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1591224&view=ms.vss-test-web.build-test-results-tab&runId=43924558&resultId=100058)|dotnet/aspnetcore#69198|
#### Summary
|24-Hour Hit Count|7-Day Hit Count|1-Month Count|
|---|---|---|
|0|11|11|