How to not display environment variable in org-babel src block?

I want the effect of this:

#+BEGIN_SRC shell :dir src
CC=gcc-9 make
#+END_SRC

But I don’t want CC=gcc-9 to show up in the output.

Is there a way to somehow include the environment variable in the BEGIN_SRC header?

I tried this but it did not work:

#+BEGIN_SRC shell :dir src :env "CC=gcc-9"
make
#+END_SRC