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

@@ -76,7 +76,7 @@ build_flags =
 
 ; ZuluSCSI RP2040 hardware platform, based on the Raspberry Pi foundation RP2040 microcontroller
 [env:ZuluSCSI_RP2040]
-platform = raspberrypi
+platform = raspberrypi@1.7.0
 framework = arduino
 board = ZuluSCSI_RP2040
 extra_scripts = src/build_bootloader.py