Ignore pkg-config installation failure due to unmet dependencies

.github/workflows/ubuntu.yml

@@ -58,7 +58,8 @@ jobs:
           ${arch:+cross}build-essential${arch/:/-} \
           libssl-dev${arch} libyaml-dev${arch} libreadline6-dev${arch} \
           zlib1g-dev${arch} libncurses5-dev${arch} libffi-dev${arch} \
-          pkg-config${arch} bison autoconf ruby
+          bison autoconf ruby
+          sudo apt-get install -q -y pkg-config${arch} || :
       - name: git config
         run: |
           git config --global advice.detachedHead 0