RP2040: Freeze platform framework version

There is new version of rp2040 platform package (1.8.0)
which will require some small changes & testing to work.
For now keep using 1.7.0.

platformio.ini

@@ -5,7 +5,7 @@ default_envs = BlueSCSI_Pico
 
 ; BlueSCSI RP2040 hardware platform, based on the Raspberry Pi foundation RP2040 microcontroller
 [env:BlueSCSI_Pico]
-platform = raspberrypi
+platform = raspberrypi@1.7.0
 platform_packages = platformio/toolchain-gccarmnoneeabi@1.100301.220327 ; toolchain-gccarmnoneeabi@1.60301.0
 framework = arduino
 board = BlueSCSI_RP2040