Ensure fresh environment for each test case in formatter tests

This commit updates `formatter_test.go` to address an issue where each test case was not receiving a fresh `formatEnvironment`. Previously, a single `formatEnvironment` instance was reused across multiple test cases, leading to potential dependencies on prior tests' states, such as indentation levels, that could result in unintended test failures.

internal/formatter/formatter_test.go

@@ -137,7 +137,6 @@ func TestFormat(t *testing.T) {
 		LowerCase:        false,
 		IdentifierQuoted: false,
 	}
-	env := &formatEnvironment{}
 	for _, fname := range files {
 		b, err := os.ReadFile(fname)
 		if err != nil {
@@ -147,6 +146,7 @@ func TestFormat(t *testing.T) {
 		if err != nil {
 			t.Fatal(err)
 		}
+		env := &formatEnvironment{}
 		formatted := Eval(parsed, env)
 		got := strings.TrimRight(formatted.Render(opts), "\n") + "\n"