"Collection was modified" exception because of transitive project references

### Preconditions
I have 3 projects:
1. Common.csproj
```xml

netstandard2.0

```
2. Lib.csproj (referenes Common.csproj)
```xml

netstandard2.0

```
3. App.csproj (references Lib.csproj)
```xml

netstandard2.0

```

I performed packages restore and build all these projects.
Everything is ok so far.

### The issue

I want to build only **Common.csproj** and **App.csproj** and obtain some data via MsBuild API. I do it in the next way:
```C#

void Run()
{
...
DoBuildProject(commonXml);
DoBuildProject(appXml);
}

void DoBuildProject(ProjectRootElement xml)
{
var properties = new Dictionary();
properties["BuildProjectReferences"] = "False";
properties["TargetFramework"] = "netstandard2.0";

var project = new Project(xml, properties, null, ProjectCollection);
var projectInstance = BuildManager.GetProjectInstanceForBuild(project);
var buildRequestData = new BuildRequestData(projectInstance, new[] { "Build" }, HostServices, BuildRequestDataFlags.ProvideProjectStateAfterBuild);
var request = BuildManager.PendBuildRequest(buildRequestData);
request.ExecuteAsync(submission =>
{
foreach (var item in submission.BuildResult.ProjectStateAfterBuild.Items)
{
...
}
}, null);
```

And from time to time I get **Collection was modified** exception. That happens when "Common" project was already built and it's items are processed inside foreach loop. But at the same time "App" project is building and modifying the "Common" project instance.

As far as I understand MsBuild builds some targets (_GetTargetFrameworks_ for example) from project references (transitive). And I can not disable this by _BuildProjectReferences_ property.

My first idea was build a project graph, but it the case above "App" project has only one project reference to "Lib" project after evaluation. The "Common" reference is added in the _IncludeTransitiveProjectReferences_ target during build process.

So maybe you have an idea how to avoid concurrent project modifications in this case.
Thanks in advance!

### Environment data
`msbuild /version` output:
15.6.85.37198

OS info:
Windows 10 Pro, x64, build 17134.112