fix: replace os.Setenv with t.Setenv in tests (usetesting)

Replace os.Setenv calls with t.Setenv in test functions to ensure
proper test environment cleanup and better test isolation.

internal/secret/debug_test.go

@@ -3,7 +3,6 @@ package secret
 import (
 	"bytes"
 	"log/slog"
-	"os"
 	"strings"
 	"syscall"
 	"testing"
@@ -12,17 +11,8 @@ import (
 )
 
 func TestDebugLogging(t *testing.T) {
-	// Save original GODEBUG and restore it
-	originalGodebug := os.Getenv("GODEBUG")
-	defer func() {
-		if originalGodebug == "" {
-			os.Unsetenv("GODEBUG")
-		} else {
-			os.Setenv("GODEBUG", originalGodebug)
-		}
-		// Re-initialize debug system with original setting
-		InitDebugLogging()
-	}()
+	// Test cleanup handled by t.Setenv
+	defer InitDebugLogging() // Re-initialize debug system after test
 
 	tests := []struct {
 		name          string
@@ -54,10 +44,8 @@ func TestDebugLogging(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			// Set GODEBUG
-			if tt.godebug == "" {
-				os.Unsetenv("GODEBUG")
-			} else {
-				os.Setenv("GODEBUG", tt.godebug)
+			if tt.godebug != "" {
+				t.Setenv("GODEBUG", tt.godebug)
 			}
 
 			// Re-initialize debug system
@@ -104,16 +92,8 @@ func TestDebugLogging(t *testing.T) {
 
 func TestDebugFunctions(t *testing.T) {
 	// Enable debug for testing
-	originalGodebug := os.Getenv("GODEBUG")
-	os.Setenv("GODEBUG", "berlin.sneak.pkg.secret")
-	defer func() {
-		if originalGodebug == "" {
-			os.Unsetenv("GODEBUG")
-		} else {
-			os.Setenv("GODEBUG", originalGodebug)
-		}
-		InitDebugLogging()
-	}()
+	t.Setenv("GODEBUG", "berlin.sneak.pkg.secret")
+	defer InitDebugLogging() // Re-initialize after test
 
 	InitDebugLogging()