node: remove noop path.Join (ethereum#25475)

Signed-off-by: Delweng <delweng@gmail.com>

node/config_test.go

@@ -115,7 +115,7 @@ func TestNodeKeyPersistency(t *testing.T) {
 	}
 	config := &Config{Name: "unit-test", DataDir: dir, P2P: p2p.Config{PrivateKey: key}}
 	config.NodeKey()
-	if _, err := os.Stat(filepath.Join(keyfile)); err == nil {
+	if _, err := os.Stat(keyfile); err == nil {
 		t.Fatalf("one-shot node key persisted to data directory")
 	}
 
@@ -136,7 +136,7 @@ func TestNodeKeyPersistency(t *testing.T) {
 	// Configure a new node and ensure the previously persisted key is loaded
 	config = &Config{Name: "unit-test", DataDir: dir}
 	config.NodeKey()
-	blob2, err := os.ReadFile(filepath.Join(keyfile))
+	blob2, err := os.ReadFile(keyfile)
 	if err != nil {
 		t.Fatalf("failed to read previously persisted node key: %v", err)
 	}