Ensure synthesized test dependencies are not satisfied by versioned Provides

The test dependencies get installed by first unpacking an
"autopkgtest-satdep" package and then calling 'apt-get --fix-broken'.
They can therefore be satisfied by virtual packages, which is not
desirable if the test dependency was specified with the special
'@' notation for pulling in the actual generated binary package.

Adding an explicit 'apt-get install' call for these packages
after the '--fix-broken' phase fixes this.

Closes: #867081