manifestgen: pass missing repoConfig to preManifest.Serialize()

When depsolve is run it returns a list of packageSpecs and the
matching repository config. This repo config is different/distinct
from the repository config that is passed into depsolve via the
package sets or the repositories that are loaded via the
reporegistry and needs to be passed into `manifest.Serialize()`.

The key different is that the depsovle `repoConfig` contains
the repo.Id that match the packageSpec.RepoId. With those two
matching IDs we can use librepo (see osbuild PR#1974) to infere
what mirror to use for what package.

This commit now passes the correct repoConfig into
preManifest.Serialize() now.

No test (sorry!) as this is really hard to test in isolation, there
is nothing observable today from repoConfig and it is impossible
to add a "witness" pipelien that could check that the right argument
is passed in `pipeline.serializeStart()`. So until we refactor
images you will have to take my word for this (sorry again).

internal/manifestgen/manifestgen.go

@@ -165,7 +165,7 @@ func (mg *Generator) Generate(bp *blueprint.Blueprint, dist distro.Distro, imgTy
 		// what are these warnings?
 		return fmt.Errorf("warnings during manifest creation: %v", strings.Join(warnings, "\n"))
 	}
-	packageSpecs, _, err := mg.depsolver(mg.cacheDir, preManifest.GetPackageSetChains(), dist, a.Name())
+	packageSpecs, repoConfig, err := mg.depsolver(mg.cacheDir, preManifest.GetPackageSetChains(), dist, a.Name())
 	if err != nil {
 		return err
 	}
@@ -177,7 +177,7 @@ func (mg *Generator) Generate(bp *blueprint.Blueprint, dist distro.Distro, imgTy
 	if err != nil {
 		return err
 	}
-	mf, err := preManifest.Serialize(packageSpecs, containerSpecs, commitSpecs, nil)
+	mf, err := preManifest.Serialize(packageSpecs, containerSpecs, commitSpecs, repoConfig)
 	if err != nil {
 		return err
 	}