Add OpenSUSE Leap 15.5 to ci

This also adds 15.4 to the list of distributions that are skipped by
default - let me know if this is not a good idea. I assume that by now
most people will be running 15.5 (15.4 will be EOL in ~3 months).

(cherry picked from commit 4ad2a6ab9a)

.cirrus.yml

@@ -249,6 +249,14 @@ opensuse_leap_15_4_task:
     dockerfile: ci/opensuse-leap-15.4/Dockerfile
     << : *RESOURCES_TEMPLATE
   << : *CI_TEMPLATE
+  << : *SKIP_TASK_ON_PR
+
+opensuse_leap_15_5_task:
+  container:
+    # Opensuse Leap 15.5 EOL: ~Dec 2024
+    dockerfile: ci/opensuse-leap-15.5/Dockerfile
+    << : *RESOURCES_TEMPLATE
+  << : *CI_TEMPLATE
 
 opensuse_tumbleweed_task:
   container:

ci/opensuse-leap-15.5/Dockerfile

@@ -0,0 +1,38 @@
+FROM opensuse/leap:15.5
+
+# A version field to invalidate Cirrus's build cache when needed, as suggested in
+# https://github.com/cirruslabs/cirrus-ci-docs/issues/544#issuecomment-566066822
+ENV DOCKERFILE_VERSION 20230905
+
+RUN zypper addrepo https://download.opensuse.org/repositories/openSUSE:Leap:15.5:Update/standard/openSUSE:Leap:15.5:Update.repo \
+ && zypper refresh \
+ && zypper in -y \
+    bison \
+    ccache \
+    cmake \
+    curl \
+    flex \
+    gcc12 \
+    gcc12-c++ \
+    git \
+    gzip \
+    libopenssl-devel \
+    libpcap-devel \
+    make \
+    python311 \
+    python311-devel \
+    python311-pip \
+    swig \
+    tar \
+    which \
+    zlib-devel \
+  && rm -rf /var/cache/zypp
+
+RUN update-alternatives --install /usr/bin/pip3 pip3 /usr/bin/pip3.11 100
+RUN update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.11 100
+RUN update-alternatives --install /usr/bin/python3-config python3-config /usr/bin/python3.11-config 100
+
+RUN pip3 install websockets junit2html
+
+RUN update-alternatives --install /usr/bin/cc cc /usr/bin/gcc-12 100
+RUN update-alternatives --install /usr/bin/c++ c++ /usr/bin/g++-12 100