codal_app: Update codal-microbit-v2 to v0.2.26.

Changes are:

codal-microbit-v2:
- Mixer: add isSilent() and fire SOUND/SILENCE events
- Introduction of persistent logging API

codal-core:
- add default atomic operations for reference counted types
- add events to CodalUSB
- ifguard uf2_info in GhostFAT implementation

codal-nrf52:
- USB for the nrf52 family
- NRF52Serial - Avoid overwriting pin definitions during redirection
- NRF52Serial::configurePins - wait for TX buffer to empty
- NRF52ADC: Improvements to discrete sampling
- NRF52I2C Workaround for missed SHORT trigger

Signed-off-by: Damien George <damien@micropython.org>

src/codal_app/codal.json

@@ -2,7 +2,7 @@
     "target": {
         "name": "codal-microbit-v2",
         "url": "https://github.com/lancaster-university/codal-microbit-v2",
-        "branch": "v0.2.25",
+        "branch": "v0.2.26",
         "type": "git",
         "test_ignore": true
     } ,