Use zsh, and ensure our ubuntu box has it

.github/workflows/ci.yml

@@ -51,6 +51,8 @@ jobs:
     steps:
       - name: Checkout Repo
         uses: actions/checkout@v4
+      - name: Install zsh
+        run: sudo apt-get install -y zsh
       - name: Setup Swift Environment
         uses: swift-actions/setup-swift@v1
         with:

Scripts/prepare-coverage-reports.sh

@@ -1,4 +1,4 @@
-#!/bin/bash -l
+#!/bin/zsh -l
 set -e
 
 function exportlcov() {