fix(arduino): Fix test path

Author: lucasssvaz

pytest-embedded-arduino/tests/test_arduino.py

@@ -2,15 +2,18 @@
 
 
 def test_arduino_serial_flash(testdir):
-    testdir.makepyfile("""
+    testdir.makepyfile(f"""
         import pexpect
         import pytest
 
         def test_arduino_app(app, dut):
-            expected_bin = os.path.join(
-                testdir.tmpdir,
-                'hello_world_arduino/build/hello_world_arduino.ino.merged.bin'
-            )
+            expected_bin = os.path.join({
+                os.path.join(testdir.tmpdir,
+                    'hello_world_arduino',
+                    'build',
+                    'hello_world_arduino.ino.merged.bin'
+                )
+            })
             assert app.binary_file == expected_bin
             assert app.target == 'esp32'
             expected_fqbn = (