[Bug] Custom source generator in solution

[BernhardGlueck]

When generating documentation for a solution that has a source generator as project which is used by other projects in the same solution the build fails as the source generator never runs.

To Reproduce
Steps to reproduce the behavior:

1. Add a custom source generator to your solution
2. Make another project in the solution use it

Expected behavior
Should have the same behaviour as dotnet build does.

Context (please complete the following information):

• OS: Linux ( Fedora 42 )
• Docfx version: 2.78.3+850a61c2ecb83b0bda21448f1393e480934556fd

[filzrev]

When generating documentation for a solution that has a source generator as project which is used by other projects in the same solution the build fails as the source generator never runs.

Is it failed when running dotnet build -c Release before running docfx command? (See: #9619 (comment))

If it failed. Please provide minimum code that reproduce issues.