tests: Four typos in tests directory.

Found by codespell.

Signed-off-by: Christian Clauss <cclauss@me.com>

tests/README.md

@@ -13,7 +13,7 @@ target platform and run the appropriate set of tests for that platform.  For exa
 
 That will run tests on the `/dev/ttyACM0` serial port.  You can also use shortcut
 device names like `a<n>` for `/dev/ttyACM<n>` and `c<n>` for `COM<n>`.  Use
-`./run-tests.py --help` to see all of the device possibilites, and other options.
+`./run-tests.py --help` to see all of the device possibilities, and other options.
 
 There are three kinds of tests:
 

tests/extmod_hardware/machine_pwm.py

@@ -1,4 +1,4 @@
-# Test machine.PWM, frequncy and duty cycle (using machine.time_pulse_us).
+# Test machine.PWM, frequency and duty cycle (using machine.time_pulse_us).
 #
 # IMPORTANT: This test requires hardware connections: the PWM-output and pulse-input
 # pins must be wired together (see the variable `pwm_pulse_pins`).

tests/ports/esp32/esp32_nvs.py

@@ -4,7 +4,7 @@ from esp32 import NVS
 
 nvs = NVS("mp-test")
 
-# test setting and gettin an integer kv
+# test setting and getting an integer kv
 nvs.set_i32("key1", 1234)
 print(nvs.get_i32("key1"))
 nvs.set_i32("key2", -503)

tests/run-tests.py

@@ -848,7 +848,7 @@ def run_tests(pyb, tests, args, result_dir, num_threads=1):
         test_file_abspath = os.path.abspath(test_file).replace("\\", "/")
 
         if args.filters:
-            # Default verdict is the opposit of the first action
+            # Default verdict is the opposite of the first action
             verdict = "include" if args.filters[0][0] == "exclude" else "exclude"
             for action, pat in args.filters:
                 if pat.search(test_file):