Add punctuation to docstrings

hardware-specific-tests/picamera2/test_exposure_time_drift.py

@@ -18,7 +18,7 @@ logging.basicConfig(level=logging.DEBUG)
 
 
 def _test_exposure_time_drift(desired_time):
-    """Capture 10 full resolution images and check that the exposure time remains constant
+    """Capture 10 full resolution images and check that the exposure time remains constant.
 
     This confirms that automatic exposure time adjustment is fully turned off
     """

hardware-specific-tests/picamera2/test_sensor_mode.py

@@ -12,7 +12,7 @@ logging.basicConfig(level=logging.DEBUG)
 
 
 def test_sensor_mode():
-    """Test capturing raw arrays in two different sensor modes"""
+    """Test capturing raw arrays in two different sensor modes."""
     cam = StreamingPiCamera2()
     server = ThingServer()
     server.add_thing(cam, "/camera/")

hardware-specific-tests/picamera2/test_tuning.py

@@ -1,4 +1,4 @@
-"""Tests that check that a tuning file can be reloaded"""
+"""Tests that check that a tuning file can be reloaded."""
 
 import os