add toolchain-test repo for gcc10

.drone.yml

@@ -182,6 +182,7 @@ steps:
     COMMON_FLAGS: 'USE_OPENMP=1'
   commands:
     - echo "MAKE_FLAGS:= $COMMON_FLAGS"
+    - add-apt-repository ppa:ubuntu-toolchain-r/test
     - apt-get update -y
     - apt-get install -y make $CC gfortran-10 perl python g++-10
     - $CC --version