fix: recursive config failure on windows

Fix failure with "package not found in config" on Windows due to
use of backslash in package name instead of forward slash, resulting
in the configuration for the sub package not being found.

Fixes: #727

pkg/config/config.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"path/filepath"
 	"reflect"
 	"regexp"
 	"strings"
@@ -661,7 +662,7 @@ func (c *Config) subPackages(
 			return nil, fmt.Errorf("failed to make subroot relative to root: %w", err)
 		}
 		absolutePackageName := packageRootName.Join(relativeFilesystemPath.Parts()...)
-		subPackages = append(subPackages, absolutePackageName.String())
+		subPackages = append(subPackages, filepath.ToSlash(absolutePackageName.String()))
 	}
 
 	return subPackages, nil