Print out which project file we're using by default (fix #8519)

cabal-install/src/Distribution/Client/ProjectPlanning.hs

...PackageTests/Backpack/Includes2/cabal-external-target.out

...tsuite/PackageTests/Backpack/Includes2/cabal-external.out

...PackageTests/Backpack/Includes2/cabal-internal-target.out

...tsuite/PackageTests/Backpack/Includes2/cabal-internal.out

cabal-testsuite/PackageTests/Backpack/Includes2/cov.out

...tsuite/PackageTests/Backpack/Includes3/cabal-external.out

...tsuite/PackageTests/Backpack/Includes3/cabal-internal.out

...-testsuite/PackageTests/Backpack/Includes3/cabal-repo.out

cabal-testsuite/PackageTests/Backpack/Reexport2/cabal.out

cabal-testsuite/PackageTests/Backpack/T6385/cabal.out

cabal-testsuite/PackageTests/Backpack/bkpcabal01/cabal.out

...testsuite/PackageTests/BuildAutogenPackageGuard/cabal.out

cabal-testsuite/PackageTests/BuildDeps/DepCycle/cabal.out

...stsuite/PackageTests/BuildDeps/InternalLibrary1/cabal.out

...dTargets/UseLocalPackage/use-local-version-of-package.out

...seLocalPackageForSetup/use-local-package-as-setup-dep.out

cabal-testsuite/PackageTests/BuildToolDepends/setup.out

cabal-testsuite/PackageTests/BuildTools/External/cabal.out

cabal-testsuite/PackageTests/BuildTools/Internal/cabal.out