RP2040: Fix use of deprecated volatile semantics for C++20 (#1318) (#… #3087

Job	Run time
GCC MicroBlaze Toolchain	4m 24s
GNU MSP430 Toolchain	1m 32s
WIN32 MingW	2m 40s
WIN32 MSVC	2m 30s
CMake Example with Native GCC	1m 16s
Native GCC (macos-latest)	3m 12s
Native GCC (ubuntu-latest)	1m 26s
GNU ARM Toolchain	2m 49s
	19m 49s

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