Static graph build hangs when a project references both an outer build and an inner build directly

A static graph build hangs during graph construction when one project references both a multi-targeted project's outer build and one of its inner builds directly. A normal build succeeds.

Related to #7432, which reported the same underlying internal error but was closed after it was no longer reproducible.

## Repro

`root.proj`:

```xml

```

`child.proj`:

```xml

TargetFramework
TargetFrameworks
net8.0;net9.0

```

Run:

```bash
dotnet msbuild root.proj /graphBuild /isolateProjects /nr:false /v:minimal
```

## Expected behavior

The graph build completes, or reports an actionable error and exits.

## Actual behavior

The process makes no progress after:

```text
Static graph construction started.
```

The underlying assertion is:

```text
Only transitive references may reference inner builds that got generated by outer builds
```

Reproduced with .NET SDK `11.0.100-preview.7.26360.111` and MSBuild `18.10.0-1.26360.111+50dbab4de`.

A Debug build from current `main` aborts at `Debug.Fail`; setting `MSBUILDDONOTLAUNCHDEBUGGER=1` makes the same build hang, confirming the exception-handling path is responsible for the differing behavior.

*This content was created with assistance from AI.*