GHA: also build with LibreSSL which is used on OpenBSD

.github/workflows/libressl.bash

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+#!/bin/bash
+set -exo pipefail
+
+export PATH="/usr/lib/ccache:$PATH"
+export CCACHE_DIR="$(pwd)/ccache"
+export CTEST_OUTPUT_ON_FAILURE=1
+
+apt-get update
+
+DEBIAN_FRONTEND=noninteractive apt-get install --no-install-{recommends,suggests} -y \
+  bison ccache cmake flex g++ lib{boost-all,ssl}-dev ninja-build tzdata
+
+mkdir build
+cd build
+
+cmake \
+  -GNinja \
+  -DCMAKE_BUILD_TYPE=Release \
+  -DICINGA2_UNITY_BUILD=ON \
+  -DUSE_SYSTEMD=OFF \
+  -DICINGA2_WITH_{MYSQL,PGSQL,COMPAT,LIVESTATUS,PERFDATA,ICINGADB}=OFF \
+  -DICINGA2_USER=$(id -un) \
+  -DICINGA2_GROUP=$(id -gn) \
+  ..
+
+ninja
+ninja test
+ninja install
+
+icinga2 daemon -C

.github/workflows/libressl.yml

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+name: LibreSSL
+
+on:
+  push:
+    branches:
+      - master
+      - 'support/*'
+  pull_request: {}
+
+concurrency:
+  group: libressl-${{ github.event_name == 'push' && github.sha || github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  libressl:
+    name: LibreSSL
+    runs-on: ubuntu-22.04
+
+    steps:
+      - name: Checkout HEAD
+        uses: actions/checkout@v3
+
+      - name: Restore/backup ccache
+        uses: actions/cache@v3
+        with:
+          path: ccache
+          key: ccache/libressl
+
+      - name: Build
+        run: .github/workflows/libressl.bash