Install Mono on macOS CI

Author: bradwilson

.github/workflows/pull-request.yaml

@@ -31,7 +31,7 @@ jobs:
       - name: Get .NET information
         run: dotnet --info
 
-      - name: Install Mono
+      - name: Install Mono (Ubuntu)
         run: >
           sudo apt-get -y install apt-transport-https dirmngr gnupg ca-certificates software-properties-common &&
           curl 'https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x3fa7e0328081bff6a14da29aa6a19b38d3d831ef' | sudo tee /etc/apt/trusted.gpg.d/mono-official-stable.asc &&
@@ -40,6 +40,10 @@ jobs:
           sudo apt-get -y install mono-complete mono-vbnc
         if: ${{ matrix.os == 'ubuntu-latest' }}
 
+      - name: Install Mono (macOS)
+        run: brew install mono
+        if: ${{ matrix.os == 'macOS-latest' }}
+
       - name: Get Mono information
         run: mono --version
         if: ${{ matrix.os != 'windows-latest' }}