feat(CI): C++20 build (#8952)

.github/workflows/cpp20.yml

@@ -0,0 +1,45 @@
+name: C++20
+on:
+  push:
+    branches:
+      - 'master'
+  pull_request:
+
+concurrency:
+  group: ${{ github.head_ref }} || concat(${{ github.ref }}, ${{ github.workflow }})
+  cancel-in-progress: true
+
+jobs:
+  build:
+    runs-on: ubuntu-20.04
+    name: C++20
+    env:
+      COMPILER: clang
+      ENABLE_CPP_20: 1
+    if: github.repository == 'azerothcore/azerothcore-wotlk'
+    steps:
+      - uses: actions/checkout@v2
+      - name: Cache
+        uses: actions/cache@v2
+        with:
+          path: var/ccache
+          key: ccache:C++20:${{ github.ref }}:${{ github.sha }}
+          restore-keys: |
+            ccache:C++20:${{ github.ref }}
+            ccache:C++20
+      - name: Configure OS
+        run: source ./acore.sh install-deps
+        env:
+          CONTINUOUS_INTEGRATION: true
+      - name: Create conf/config.sh
+        run: source ./apps/ci/ci-conf.sh
+      - name: Import db
+        run: source ./apps/ci/ci-import-db.sh
+      - name: Build
+        run: source ./apps/ci/ci-compile.sh
+      - name: Dry run
+        run: source ./apps/ci/ci-worldserver-dry-run.sh
+      - name: Check startup errors
+        run: source ./apps/ci/ci-error-check.sh
+      - name: Run unit tests
+        run: source ./apps/ci/ci-run-unit-tests.sh