fix(build): freezing Niels Lohmann JSON version to v3.10.3

Signed-off-by: Raphael Defosseux <raphael.defosseux@eurecom.fr>

build/scripts/build_helper.nrf

@@ -141,7 +141,6 @@ install_pistache_from_git() {
     fi
 
     git clone $GIT_URL
-    git submodule update --init
     cd pistache && git checkout e18ed9baeb2145af6f9ea41246cf48054ffd9907
     ret=$?;[[ $ret -ne 0 ]] && popd && return $ret
     mkdir _build && cd _build
@@ -191,8 +190,7 @@ install_nlohmann_from_git() {
     fi
 
     git clone $GIT_URL
-    git submodule update --init
-    cd json && git checkout master
+    cd json && git checkout -f v3.10.3
     ret=$?;[[ $ret -ne 0 ]] && popd && return $ret
     mkdir _build && cd _build
     $CMAKE -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=Release -DJSON_BuildTests=OFF ..