ci: limit parallel jobs in Drone

.drone/drone.sh

@@ -174,6 +174,8 @@ if [ "$DRONE_JOB_BUILDTYPE" == "boost" ]; then
 
   echo '==================================> SCRIPT'
 
+  export B2_JOBS=4
+
   # export B2_TARGETS=${B2_TARGETS:-"libs/$SELF/test libs/$SELF/example"}
   if [ -n "$COMPILER" ] && [ -n "$B2_TOOLSET" ]; then
     echo "using $B2_TOOLSET : : $COMPILER ;" >> ~/user-config.jam

tools/build-and-test.sh

@@ -23,7 +23,7 @@ elif [[ "${TRAVIS}" == "true" ]]; then
   JOBS="2"
 elif [[ $(uname -s) == "Linux" ]]; then
   # Physical cores
-  JOBS=$(lscpu -p | grep -v '^#' | sort -u -t, -k 2,4 | wc -l)
+  JOBS=4
 elif [[ $(uname) == "Darwin" ]]; then
   # Physical cores
   JOBS=$(sysctl -n hw.physicalcpu)