Repair YAML typo in CI

Author: ckormanyos

.github/workflows/multiprecision.yml

@@ -158,7 +158,7 @@ jobs:
         with:
           fetch-depth: '0'
       - name: Set TOOLSET
-        run: echo ${{ matrix.compiler }} | awk '/^g/ { print "TOOLSET=gcc" } /^clang/ { print "TOOLSET=clang" }' >> $GITHUB_ENV
+        run: echo g++ | awk '/^g/ { print "TOOLSET=gcc" } /^clang/ { print "TOOLSET=clang" }' >> $GITHUB_ENV
       - name: Add repository
         continue-on-error: true
         id: addrepo
@@ -234,7 +234,7 @@ jobs:
         if: steps.retry1.outcome=='failure'
         run: sudo apt-add-repository -y "ppa:ubuntu-toolchain-r/test"
       - name: Install packages
-        run: sudo apt install g++-10 g++-11 clang-10 clang-11 libgmp-dev libmpfr-dev libtommath-dev libeigen3-dev libmpfi-dev libmpc-dev
+        run: sudo apt install g++-9 g++-10 g++-11 clang-10 clang-11 libgmp-dev libmpfr-dev libtommath-dev libeigen3-dev libmpfi-dev libmpc-dev
       - name: Checkout main boost
         run: git clone -b develop --depth 1 https://github.com/boostorg/boost.git ../boost-root
       - name: Update tools/boostdep