Codechange: [CI] build some targets every night, instead of every PR

This mainly as they are not expected to fail, or give more information
than the other targets already would. And this is just hogging up
the CI pipeline. On average, these targets take ~80 CPU-minutes to
finish.

.github/workflows/ci-nightly.yml

@@ -0,0 +1,82 @@
+name: CI - Nightly
+
+on:
+  schedule:
+  - cron: '0 3 * * *'
+  workflow_dispatch:
+
+env:
+  CTEST_OUTPUT_ON_FAILURE: 1
+
+jobs:
+  linux:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+        - name: GCC - SDL1.2
+          compiler: gcc
+          cxxcompiler: g++
+          libraries: libsdl1.2-dev
+
+    name: Linux (${{ matrix.name }})
+
+    uses: ./.github/workflows/ci-linux.yml
+    secrets: inherit
+
+    with:
+      compiler: ${{ matrix.compiler }}
+      cxxcompiler: ${{ matrix.cxxcompiler }}
+      libraries: ${{ matrix.libraries }}
+      extra-cmake-parameters:
+
+  macos:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+        - arch: x64
+          full_arch: x86_64
+
+    name: Mac OS (${{ matrix.arch }})
+
+    uses: ./.github/workflows/ci-macos.yml
+    secrets: inherit
+
+    with:
+      arch: ${{ matrix.arch }}
+      full_arch: ${{ matrix.full_arch }}
+
+  mingw:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+        - msystem: MINGW64
+          arch: x86_64
+        - msystem: MINGW32
+          arch: i686
+
+    name: MinGW (${{ matrix.arch }})
+
+    uses: ./.github/workflows/ci-mingw.yml
+    secrets: inherit
+
+    with:
+      msystem: ${{ matrix.msystem }}
+      arch: ${{ matrix.arch }}
+
+  check_annotations:
+    name: Check Annotations
+    needs:
+    - linux
+    - macos
+    - mingw
+
+    if: always()
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Check annotations
+      uses: OpenTTD/actions/annotation-check@v5