GHA: Fix Alpine LibreSSL

First, the icinga_legacytimeperiod/dst test was excluded, as it fails on
Alpine most likely due to some differences between musl and glibc. After
some debugging, I disabled the test as the Alpine packages does.

More build dependencies were added from the Alpine package, allowing to
only disable MySQL and PostgreSQL support as these libraries have fixed
dependencies on OpenSSL, conflicting with LibreSSL.

In addition, I have added comments where I was first puzzled.

.github/workflows/alpine-bash.Dockerfile

@@ -1,2 +1,8 @@
+# This Dockerfile is used in the linux job for Alpine Linux.
+#
+# As the linux.bash script is, in fact, a bash script and Alpine does not ship
+# a bash by default, the "alpine:bash" container will be built using this
+# Dockerfile in the GitHub Action.
+
 FROM alpine:3
 RUN ["apk", "--no-cache", "add", "bash"]

.github/workflows/linux.bash

@@ -8,9 +8,19 @@ CMAKE_OPTS=''
 
 case "$DISTRO" in
   alpine:*)
-    apk add bison {boost,libressl}-dev ccache cmake flex g++ ninja-build tzdata
+    # Packages inspired by the Alpine package, just
+    # - LibreSSL instead of OpenSSL 3 and
+    # - no MariaDB or libpq as they depend on OpenSSL.
+    # https://gitlab.alpinelinux.org/alpine/aports/-/blob/master/community/icinga2/APKBUILD
+    apk add bison boost-dev ccache cmake flex g++ libedit-dev libressl-dev ninja-build tzdata
     ln -vs /usr/lib/ninja-build/bin/ninja /usr/local/bin/ninja
-    CMAKE_OPTS="-DUSE_SYSTEMD=OFF $(echo -DICINGA2_WITH_{MYSQL,PGSQL,COMPAT,LIVESTATUS,PERFDATA,ICINGADB}=OFF)"
+
+    CMAKE_OPTS="-DUSE_SYSTEMD=OFF -DICINGA2_WITH_MYSQL=OFF -DICINGA2_WITH_PGSQL=OFF"
+
+    # This test fails due to some glibc/musl mismatch regarding timezone PST/PDT.
+    # - https://www.openwall.com/lists/musl/2024/03/05/2
+    # - https://gitlab.alpinelinux.org/alpine/aports/-/blob/b3ea02e2251451f9511086e1970f21eb640097f7/community/icinga2/disable-failing-tests.patch
+    sed -i '/icinga_legacytimeperiod\/dst$/d' /icinga2/test/CMakeLists.txt
     ;;
 
   amazonlinux:2)

.github/workflows/linux.yml

@@ -21,7 +21,10 @@ jobs:
       max-parallel: 2
       matrix:
         distro:
-          - alpine:bash # LibreSSL, used on OpenBSD
+          # Alpine Linux to build Icinga 2 with LibreSSL, OpenBSD's default.
+          # The "alpine:bash" image will be built below based on "alpine:3".
+          - alpine:bash
+
           - amazonlinux:2
           - amazonlinux:2023
 
@@ -60,7 +63,7 @@ jobs:
           path: ccache
           key: ccache/${{ matrix.distro }}
 
-      - name: Build Docker image
+      - name: Build Alpine Docker Image
         if: "matrix.distro == 'alpine:bash'"
         run: >-
           docker build --file .github/workflows/alpine-bash.Dockerfile