test: isolates temp test fixtures (#1569)

## Motivation and Context

Replace shared temp paths with `t.TempDir()`` so each test gets its own
cleanup-scoped directory.
- This avoids leftover files and cross-test interference. No production
code changed.

## How Has This Been Tested?

GitHub CI passed.
- https://github.com/yowainwright/registry/pull/1

## Breaking Changes

No breaking changes; just tests.

## Types of changes

- [x] chore

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed

## Additional context

Small test-only cleanup. No production code paths are changed.

Co-authored-by: Radoslav Dimitrov <radoslav@stacklok.com>

internal/importer/importer_test.go

@@ -20,8 +20,7 @@ import (
 )
 
 func TestImportService_LocalFile(t *testing.T) {
-	// Create a temporary seed file
-	tempFile := filepath.Join(os.TempDir(), "test_import_seed.json")
+	tempFile := filepath.Join(t.TempDir(), "test_import_seed.json")
 	seedData := []*apiv0.ServerJSON{
 		{
 			Schema:      model.CurrentSchemaURL,
@@ -41,7 +40,6 @@ func TestImportService_LocalFile(t *testing.T) {
 
 	err = os.WriteFile(tempFile, jsonData, 0600)
 	require.NoError(t, err)
-	defer os.Remove(tempFile)
 
 	// Create registry service
 	testDB := database.NewTestDB(t)
@@ -187,6 +185,14 @@ func TestImportService_ErrorHandling(t *testing.T) {
 	registryService := service.NewRegistryService(testDB, &config.Config{EnableRegistryValidation: false})
 	importerService := importer.NewService(registryService)
 
+	errorDir := t.TempDir()
+	missingFile := filepath.Join(errorDir, "non-existent-file.json")
+	invalidFile := filepath.Join(errorDir, "invalid.json")
+
+	invalidJSON := []byte("{invalid json}")
+	err := os.WriteFile(invalidFile, invalidJSON, 0600)
+	require.NoError(t, err)
+
 	tests := []struct {
 		name        string
 		path        string
@@ -195,13 +201,13 @@ func TestImportService_ErrorHandling(t *testing.T) {
 	}{
 		{
 			name:        "non-existent local file",
-			path:        "/tmp/non-existent-file.json",
+			path:        missingFile,
 			expectError: true,
 			errorMsg:    "failed to read seed data",
 		},
 		{
 			name:        "invalid JSON file",
-			path:        "/tmp/invalid.json",
+			path:        invalidFile,
 			expectError: true,
 			errorMsg:    "failed to read seed data",
 		},
@@ -213,22 +219,6 @@ func TestImportService_ErrorHandling(t *testing.T) {
 		},
 	}
 
-	// Create invalid JSON file for testing
-	invalidJSON := []byte("{invalid json}")
-	tempFile, err := os.CreateTemp("", "invalid-*.json")
-	require.NoError(t, err)
-	defer os.Remove(tempFile.Name())
-	err = os.WriteFile(tempFile.Name(), invalidJSON, 0600)
-	require.NoError(t, err)
-
-	// Update test case to use temp file
-	for i := range tests {
-		if tests[i].path == "/tmp/invalid.json" {
-			tests[i].path = tempFile.Name()
-			break
-		}
-	}
-
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			err := importerService.ImportFromPath(context.Background(), tt.path)