CI: Install meson and ninja for macOS

Meson and Ninja are used by picolibc. Explicitly install these tools
which we appear to have been getting by some transitive dependency up to
now.

Signed-off-by: Chris Packham <judge.packham@gmail.com>

.github/workflows/continuous-integration-workflow.yml

@@ -22,7 +22,7 @@ jobs:
         if: ${{ runner.os == 'macOS' }}
         run: |
           brew install autoconf automake bash binutils gawk gnu-sed \
-               gnu-tar help2man make ncurses texinfo libtool
+               gnu-tar help2man libtool make meson ncurses ninja texinfo
       - name: "build ct-ng"
         run: |
           if [ "$RUNNER_OS" == "macOS" ]; then