test(semantic): include ecosystems not supported by lockfile (#1364)

Notably this adds coverage over the Ubuntu entry, since that reuses
Debian so we don't have any explicit tests for that in the comparison
tests.

We also no longer need to be manually adding `CRAN` since `lockfile`
supports it

internal/semantic/parse_test.go

@@ -14,8 +14,7 @@ func TestParse(t *testing.T) {
 
 	ecosystems := lockfile.KnownEcosystems()
 
-	// todo: remove once CRAN is supported by lockfile
-	ecosystems = append(ecosystems, "CRAN")
+	ecosystems = append(ecosystems, "Alpine", "Debian", "Ubuntu")
 
 	for _, ecosystem := range ecosystems {
 		_, err := semantic.Parse("", models.Ecosystem(ecosystem))
@@ -37,8 +36,7 @@ func TestMustParse(t *testing.T) {
 
 	ecosystems := lockfile.KnownEcosystems()
 
-	// todo: remove once CRAN is supported by lockfile
-	ecosystems = append(ecosystems, "CRAN")
+	ecosystems = append(ecosystems, "Alpine", "Debian", "Ubuntu")
 
 	for _, ecosystem := range ecosystems {
 		semantic.MustParse("", models.Ecosystem(ecosystem))