Update requirements.txt to solve CI build errors

use latest platformIO package, to avoid build errors due to missing 'scons'

> Tool Manager: Installing platformio/tool-scons @ ~4.40400.0 
> Error: Could not find the package with 'platformio/tool-scons @ ~4.40400.0' requirements for your system 'linux_x86_64' 

> Error: Process completed with exit code 1.

requirements.txt

@@ -36,7 +36,7 @@ marshmallow==3.19.0
     # via platformio
 packaging==23.1
     # via marshmallow
-platformio==6.1.6
+platformio==6.1.14
     # via -r requirements.in
 pyelftools==0.29
     # via platformio