Tests/CXXModules: test exporting modules which include headers
Test that headers that are part of the same target are available to modules in the target itself.
Fixes: #25909 (closed)
Backport: release
Manual-backport: release-3.28
Test that headers that are part of the same target are available to modules in the target itself.
Fixes: #25909 (closed)
Backport: release
Manual-backport: release-3.28