[Flaky Test] Microsoft.Build.UnitTests.CommunicationUtilitiesTests.GetEnvVars

**Flaky-test key** (automated de-duplication — do not edit):
```text
flaky-test-id: Microsoft.Build.UnitTests.CommunicationUtilitiesTests.GetEnvVars
```

## Evidence

- **Assembly**: `Microsoft.Build.Framework.UnitTests`
- **Fully-qualified name**: `Microsoft.Build.UnitTests.CommunicationUtilitiesTests.GetEnvVars`
- **Distinct sources**: 3 (0 PRs + 3 rolling builds)
- **Rolling builds**: [1514373](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1514373), [1517682](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1517682), [1527742](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1527742)
- **Legs**: CoreOnLinux
- **TFMs**: net10.0, net11.0
- **First seen**: 2026-07-17 | **Last seen**: 2026-07-27
- **Total failures**: 3
- **Error hashes**: 2 distinct (`20f286f7`, `dd479999`)

### Sample error

```
System.ArgumentException: An item with the same key has already been added. Key: SEMMLE_PRELOAD_LIBTRACE32
```

See [sample build](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1514373) for details.

## Action

This test will be quarantined with `[ActiveIssue("")]` (from `Microsoft.DotNet.XUnitV3Extensions`, namespace `Xunit`) until the underlying nondeterminism is fixed. The quarantine pipeline (def 344) will continue running it to gather signal.

> [!WARNING]
>
> Firewall blocked 2 domains
>
> The following domains were blocked by the firewall during workflow execution:
>
> - `awmgmcpg`
> - `southcentralus0.in.applicationinsights.azure.com`
>> To allow these domains, add them to the `network.allowed` list in your workflow frontmatter:
>
> ```yaml
> network:
> allowed:
> - defaults
> - "awmgmcpg"
> - "southcentralus0.in.applicationinsights.azure.com"
> ```
>
> See [Network Configuration](https://github.github.com/gh-aw/reference/network/) for more information.
>
>

> Generated by [Flaky Test Triage](https://github.com/dotnet/msbuild/actions/runs/30267259222) · sonnet46 · 153.8 AIC · ⌖ 6.72 AIC · ⊞ 14.7K · [◷](https://github.com/search?q=repo%3Adotnet%2Fmsbuild+is%3Aissue+%22gh-aw-workflow-call-id%3A+dotnet%2Fmsbuild%2Fflaky-test-detector.agent%22&type=issues)

Locate Microsoft.Build.UnitTests.CommunicationUtilitiesTests.GetEnvVars in the Microsoft.Build.Framework.UnitTests assembly and review the three linked rolling-build failures, starting with the duplicate SEMMLE_PRELOAD_LIBTRACE32 key. Reproduce it on the CoreOnLinux leg for net10.0 or net11.0, then verify the test no longer produces duplicate-key failures before removing its quarantine.

Written by the indexing model from the issue text.