filter out registered migrations when run against a directory without them

[prabhu-tyke]

When running a migration against a particular directory without go migrations, getting the registered migrations too. How to filter those out? #588, I see this pr addresses this but not able to make it work.

My directory structure:

migrations:
----ad-hoc:
--------1000_1000.go
----0001_1.sql
----0002_2.sql

in my main.go have imported the ad-hoc package, in .go file have done goose.AddMigrationNoTxContext(). I run my binary against ./migrations where there are only sql files. Is there a way around this?

seeing this:

	var sources []source
	for _, fullpath := range goFiles {
		v, err := NumericComponent(fullpath)
		if err != nil {
			continue // Skip any files that don't have version prefix.
		}
		if strings.HasSuffix(fullpath, "_test.go") {
			continue // Skip Go test files.
		}
		if versionFilter(v, current, target) {
			sources = append(sources, source{
				fullpath: fullpath,
				version:  v,
			})
		}
	}
	var (
		migrations Migrations
	)
	if len(sources) > 0 {
		for _, s := range sources {
			migration, ok := registeredGoMigrations[s.version]
			if ok {
				migrations = append(migrations, migration)
			}