Set up check version script, add CI workflow

.github/workflows/versions.yml

@@ -0,0 +1,10 @@
+name: Check Versions
+
+on: [ push ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - run: ./check-versions.sh

check-versions.sh

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if ( ! command -v jq > /dev/null )
+then
+  echo 'The jq command is required for this script.'
+  exit 1
+fi
+
+allMatch=1
+function checkVersionMatch() {
+    echo "- $1: $2"
+    if [ ! "$composerVersion" = "$2" ]
+    then
+      allMatch=0
+    fi
+}
+
+echo "Detected versions:"
+
+composerVersion=$(jq -r .version 'composer.json')
+checkVersionMatch 'composer.json' "$composerVersion"
+
+checkVersionMatch 'CHANGELOG.md' "$(sed -nE 's/^## (.*) -.*$/\1/p' 'CHANGELOG.md' | head -n 1)"
+
+if [ ! "$allMatch" = 1 ]
+then
+  echo 'Not all versions match.'
+  exit 1
+else
+  echo 'All version match!'
+fi