bump mbed core to latest

[umbynos]

The Board field when running arduino-fwuploader firmware list

$ arduino-fwuploader firmware list -b arduino:mbed_nano:nanorp2040connect
Board FQBN                                Module   Version
      arduino:mbed_nano:nanorp2040connect NINA     1.4.5  
      arduino:mbed_nano:nanorp2040connect NINA     1.4.6  
      arduino:mbed_nano:nanorp2040connect NINA     1.4.7  
      arduino:mbed_nano:nanorp2040connect NINA   ✔ 1.4.8

I have opened an issue on the arduino-cli repo because apparently the problem comes from it:
arduino/arduino-cli#1401

The cli is used to obtain the name of the board, by the generator, which is run by the CI in the generate-index.json workflow. This is only a temporary fix, while we wait for the fix in arduino-cli

This is the diff before and after this commit:

--- /home/umberto/Nextcloud/8tb/Lavoro/arduino-fwuploader/generator/boards/module_firmware_index.json
+++ /home/umberto/Nextcloud/8tb/Lavoro/arduino-fwuploader/generator/boards/module_firmware_index.json.new
@@ -493,6 +493,7 @@
       "size": "1674900"
     },
     "module": "NINA",
+    "name": "Arduino Nano RP2040 Connect",
     "uploader": "arduino:rp2040tools@1.0.2",
     "upload.use_1200bps_touch": true,
     "upload.wait_for_upload_port": true,