Downgrade return-mismatch error to warning (FreeRTOS#1374)

portYIELD_FROM_ISR(x) is defined as 'return x' in the Windows port which
causes compilation failures in the WIN32-MinGW demo when using GCC 14.

Failure: https://github.com/FreeRTOS/FreeRTOS-Kernel/actions/runs/18272553628/job/52017559140?pr=1317

Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>

Author: aggarg

FreeRTOS/Demo/WIN32-MingW/Makefile

@@ -3,7 +3,7 @@ BUILD_DIR := ./build
 
 # Compiler - Note this expects you are using MinGW version of GCC
 CC := gcc
-CFLAGS := -O0 -g3 -Wall -Wextra -c -fmessage-length=0 -Wcast-qual -D_WIN32_WINNT=0x0601
+CFLAGS := -O0 -g3 -Wall -Wextra -c -fmessage-length=0 -Wcast-qual -Wno-error=return-mismatch -D_WIN32_WINNT=0x0601
 
 ifeq ($(COVERAGE_TEST),1)
   CFLAGS += -DprojCOVERAGE_TEST=1