codal_app: Update codal-microbit-v2 to v0.2.40.

Changes to codal-microbit-v2 include:
- change variable sampleRate to float to avoid rounding errors when
  generating frequencies
- improve audio input pipeline for microphone support
- add per-channel volume control methods
- increase DAPLink I2C wait for data to be ready timeout
- add missing end frequency parameter to the log generator function
- add polyphonic real-time synthesizer
- fix MicroBitBLEManager support for MicroBitPowerManager::deepSleep
- add support for the BUSY flag on the KL27
- add the DAPLink version to the data logging HTM page
- add MicroBitLog::readData

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

Author: dpgeorge

src/codal_app/codal.json

@@ -2,7 +2,7 @@
     "target": {
         "name": "codal-microbit-v2",
         "url": "https://github.com/lancaster-university/codal-microbit-v2",
-        "branch": "v0.2.35",
+        "branch": "v0.2.40",
         "type": "git",
         "test_ignore": true
     } ,