ensure cppcheck is always the right version (#1843)

tests/misra/install.sh

@@ -10,7 +10,7 @@ fi
 
 cd $CPPCHECK_DIR
 VERS="2.13.0"
-git fetch origin $VERS
+git fetch --tags origin $VERS
 git checkout $VERS
-make clean
+#make clean
 make MATCHCOMPILTER=yes CXXFLAGS="-O2" -j8

tests/misra/test_misra.sh

@@ -10,7 +10,7 @@ NC='\033[0m'
 : "${CPPCHECK_DIR:=$DIR/cppcheck/}"
 
 # install cppcheck if missing
-if [ ! -d $CPPCHECK_DIR ]; then
+if [ -z "${SKIP_BUILD}" ]; then
   $DIR/install.sh
 fi