Legacy-style project referencing duplicate multi-targetting projects don't set the TF on the reference correctly.

### Issue Description
In certain scenarios, we get a `error MSB4057: The target "GetTargetPath" does not exist in the project.` due to the TF not properly being set on a project reference.

### Steps to Reproduce
Proj1\Proj1.csproj:
```xml

v4.7.2
Library

```
(Note the project references are differently-cased)

Proj2\Proj2.csproj:
```xml

netstandard2.0;net472

```

Commands:
```
msbuild /t:Restore Proj1\Proj1.csproj
msbuild Proj1\Proj1.csproj /p:BuildProjectReferences=false /bl
```

### Expected Behavior
The build succeeds.

### Actual Behavior
The build fails with `proj2\proj2.csproj : error MSB4057: The target "GetTargetPath" does not exist in the project.`

### Analysis
The specific piece of logic which is failing to run is:
```xml

TargetFramework=%(AnnotatedProjects.NearestTargetFramework)

```

That translates the `NearestTargetFramework` computed by `GetReferenceNearestTargetFrameworkTask` to `SetTargetFramework`, which is used when executing on project references.

Oddly, I couldn't seem to get this to repro if:
* Proj1 is an SDK-style project
* The duplicated `ProjectReference` did not differ in case (I guess there's some case-sensitive deduplication somewhere?)

Also note that the `/p:BuildProjectReferences=false` just helps show off the error more easily. Without it, the TF is still not properly set so the project refernce is "fully" built instead of building only 1 TF. Furthermore, I believe in this case the referenced project's assembly isn't returned so isn't actually given to the referencing project's compiler, an obvious downstream problem.

### Versions & Configurations
16.9.0-preview-21076-21+8ed151254 (but it repros for earlier versions too.)