Remove -Werror=all from build flags, but enable it in CI

Partial fix for #7024

Author: me-no-dev

.github/scripts/sketch_utils.sh

@@ -148,6 +148,7 @@ function build_sketch(){ # build_sketch <ide_path> <user_path> <path-to-ino> [ex
                 --fqbn "$currfqbn" \
                 --board-options "$curroptions" \
                 --warnings "all" \
+                --build-property "compiler.warning_flags.all=-Wall -Werror=all -Wextra" \
                 --build-cache-path "$ARDUINO_CACHE_DIR" \
                 --build-path "$build_dir" \
                 $xtra_opts "${sketchdir}"

platform.txt

@@ -118,8 +118,8 @@ compiler.size.cmd={compiler.prefix}size
 compiler.warning_flags=-w
 compiler.warning_flags.none=-w
 compiler.warning_flags.default=
-compiler.warning_flags.more=-Wall -Werror=all
-compiler.warning_flags.all=-Wall -Werror=all -Wextra
+compiler.warning_flags.more=-Wall
+compiler.warning_flags.all=-Wall -Wextra
 
 # These can be overridden in platform.local.txt
 compiler.c.extra_flags=