tools/ci: correcly report flake8 version.

If the flake8 executable is not found, the static test script reports
the tool as missing. It may happen that the flake8 module is installed,
but the console entry point is not.

In the flake8 shell script, flake is invoked via `python -m`. The result
is a confusing error message where static-test reports the tools as missing,
yet the flake8 tests are run.

This patch makes the toolchain version script use the same command as the
flake8 script.

dist/tools/ci/print_toolchain_versions.sh

@@ -111,7 +111,6 @@ for c in \
          cmake \
          cppcheck \
          doxygen \
-         flake8 \
          git \
          make \
          openocd \
@@ -121,6 +120,7 @@ for c in \
          ; do
     printf "%23s: %s\n" "$c" "$(get_cmd_version "${c}")"
 done
+printf "%23s: %s\n" "flake8" "$(get_cmd_version "python3 -Wignore -m flake8")"
 printf "%23s: %s\n" "coccinelle" "$(get_cmd_version spatch)"
 
 exit 0