dotnet format emits a warning for unsupported projects even if the project's directory is excluded

[mm-jhn]

Describe the bug

dotnet format emits a warning when the solution contains a project without a language (e.g. modelproj) that can't be suppressed even when the folder containing the project is excluded from the analysis.

To Reproduce

1. Fetch the repro at https://github.com/mm-jhn/repro-20250123/
2. Run dotnet format --verify-no-changes --exclude "DependencyValidation"

Expected: The project is ignored, no warning is emitted.
Actual: Warnings were encountered while loading the workspace. Set the verbosity option to the 'diagnostic' level to log warnings.
When you add -v diag, you get this warning:

Cannot open project 'C:\Users\[username]\source\repos\repro-20250123\DependencyValidation\DependencyValidation.modelproj' because the file extension '.modelproj' is not associated with a language.

Exceptions (if any)

None, only warnings.

Further technical details

Visual Studio 17.12.4 on Windows 11

.NET SDK:
 Version:           9.0.102
 Commit:            cb83cd4923
 Workload version:  9.0.100-manifests.4a54b1a6
 MSBuild version:   17.12.18+ed8c6aec5

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.22631
 OS Platform: Windows
 RID:         win-x64
 Base Path:   C:\Program Files\dotnet\sdk\9.0.102\

.NET workloads installed:
There are no installed workloads to display.
Configured to use loose manifests when installing new manifests.

Host:
  Version:      9.0.1
  Architecture: x64
  Commit:       c8acea2262

.NET SDKs installed:
  6.0.428 [C:\Program Files\dotnet\sdk]
  8.0.405 [C:\Program Files\dotnet\sdk]
  9.0.102 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 8.0.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 9.0.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 8.0.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 9.0.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 8.0.12 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 9.0.1 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
  x86   [C:\Program Files (x86)\dotnet]
    registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x86\InstallLocation]

Environment variables:
  Not set

global.json file:
  Not found

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  https://aka.ms/dotnet/info

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  https://aka.ms/dotnet/download