rename confusing test module name

config/module/test-fixtures/basic-parent-providers/a/a.tf

@@ -5,7 +5,7 @@ provider "bottom" {
     value = "from bottom"
 }
 
-module "b" {
+module "c" {
     source = "../c"
     providers = {
         "bottom" = "bottom.foo"

config/module/tree_test.go

@@ -542,13 +542,13 @@ func TestTreeProviders_basic(t *testing.T) {
 	}
 
 	for _, child := range a.Children() {
-		if child.Name() == "b" {
+		if child.Name() == "c" {
 			b = child
 		}
 	}
 
 	if b == nil {
-		t.Fatal("could not find module 'b'")
+		t.Fatal("could not find module 'c'")
 	}
 
 	aProviders := a.config.ProviderConfigsByFullName()