refactor: Use static_cast<decltype(...)> to suppress integer sanitizer warning

This refactor does not change any behavior, except for the integer
sanitizer warning.

Can be tested via:

UBSAN_OPTIONS="suppressions=$(pwd)/test/sanitizer_suppressions/ubsan:print_stacktrace=1:halt_on_error=1:report_error_type=1" ./bld-cmake/bin/bitcoin-cli -stdinrpcpass uptime

src/compat/stdin.cpp

@@ -43,7 +43,7 @@ void SetStdinEcho(bool enable)
         return;
     }
     if (!enable) {
-        tty.c_lflag &= ~ECHO;
+        tty.c_lflag &= static_cast<decltype(tty.c_lflag)>(~ECHO);
     } else {
         tty.c_lflag |= ECHO;
     }