ci: test building nix targets to avoid regressions

Otherwise build failure may only be detected during release.

Author: link2xt

.github/workflows/nix.yml

@@ -0,0 +1,60 @@
+name: Test Nix flake
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+jobs:
+  build:
+    name: nix build
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        installable:
+          - deltachat-python
+          - deltachat-repl
+          - deltachat-repl-aarch64-linux
+          - deltachat-repl-arm64-v8a-android
+          - deltachat-repl-armeabi-v7a-android
+          - deltachat-repl-armv6l-linux
+          - deltachat-repl-armv7l-linux
+          - deltachat-repl-i686-linux
+          - deltachat-repl-win32
+          - deltachat-repl-win64
+          - deltachat-repl-x86_64-android
+          - deltachat-repl-x86_64-linux
+          - deltachat-repl-x86-android
+          - deltachat-rpc-client
+          - deltachat-rpc-server
+          - deltachat-rpc-server-aarch64-linux
+          - deltachat-rpc-server-aarch64-linux-wheel
+          - deltachat-rpc-server-arm64-v8a-android
+          - deltachat-rpc-server-armeabi-v7a-android
+          - deltachat-rpc-server-armv6l-linux
+          - deltachat-rpc-server-armv6l-linux-wheel
+          - deltachat-rpc-server-armv7l-linux
+          - deltachat-rpc-server-armv7l-linux-wheel
+          - deltachat-rpc-server-i686-linux
+          - deltachat-rpc-server-i686-linux-wheel
+          - deltachat-rpc-server-source
+          - deltachat-rpc-server-win32
+          - deltachat-rpc-server-win32-wheel
+          - deltachat-rpc-server-win64
+          - deltachat-rpc-server-win64-wheel
+          - deltachat-rpc-server-x86_64-android
+          - deltachat-rpc-server-x86_64-linux
+          - deltachat-rpc-server-x86_64-linux-wheel
+          - deltachat-rpc-server-x86-android
+          - docs
+          - libdeltachat
+          - python-docs
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          show-progress: false
+      - uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
+      - name: Build deltachat-rpc-server binaries
+        run: nix build .#deltachat-rpc-server-${{ matrix.arch }}-linux