Pin version of z3 used for mac CI to 4.8.10

This prevents auto upgrade of z3, in order to keep it inline with the
version used on Windows. Note that the version currently being installed
on Mac is already 4.8.10.

Author: thomasspriggs

.github/workflows/pull-request-checks.yaml

@@ -177,7 +177,11 @@ jobs:
         with:
           submodules: recursive
       - name: Fetch dependencies
-        run: brew install maven flex bison parallel ccache z3
+        run: |
+          brew install maven flex bison parallel ccache
+          # The commit hash below pins z3 to version 4.8.10
+          wget https://raw.githubusercontent.com/Homebrew/homebrew-core/e2c833d326c45d9aaf4e26af6dd8b2f31564dc04/Formula/z3.rb
+          brew install --HEAD -s z3.rb
       - name: Confirm z3 solver is available and log the version installed
         run: z3 --version
       - name: Prepare ccache
@@ -219,7 +223,11 @@ jobs:
         with:
           submodules: recursive
       - name: Fetch dependencies
-        run: brew install cmake ninja maven flex bison ccache z3
+        run: |
+          brew install cmake ninja maven flex bison ccache
+          # The commit hash below pins z3 to version 4.8.10
+          wget https://raw.githubusercontent.com/Homebrew/homebrew-core/e2c833d326c45d9aaf4e26af6dd8b2f31564dc04/Formula/z3.rb
+          brew install --HEAD -s z3.rb
       - name: Confirm z3 solver is available and log the version installed
         run: z3 --version
       - name: Prepare ccache