CI: add Opensuse Leap 15.6

.cirrus.yml

@@ -126,12 +126,20 @@ debian11_static_task:
   << : *CI_TEMPLATE
   << : *SKIP_TASK_ON_PR
 
+opensuse_leap_15_6_task:
+  container:
+    # Opensuse Leap 15.6 EOL: ~Dec 2025
+    dockerfile: ci/opensuse-leap-15.6/Dockerfile
+    << : *RESOURCES_TEMPLATE
+  << : *CI_TEMPLATE
+
 opensuse_leap_15_5_task:
   container:
-    # Opensuse Leap 15.5 EOL: Around Dec 25
+    # Opensuse Leap 15.5 EOL: ~Dec 2024
     dockerfile: ci/opensuse-leap-15.5/Dockerfile
     << : *RESOURCES_TEMPLATE
   << : *CI_TEMPLATE
+  << : *SKIP_TASK_ON_PR
 
 opensuse_tumbleweed_task:
   container:

ci/opensuse-leap-15.6/Dockerfile

@@ -0,0 +1,20 @@
+FROM opensuse/leap:15.6
+
+# 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 20240524
+
+RUN zypper addrepo https://download.opensuse.org/repositories/openSUSE:Leap:15.6:Update/standard/openSUSE:Leap:15.6:Update.repo \
+ && zypper refresh \
+ && zypper in -y \
+    bison \
+    cmake \
+    flex \
+    gcc10 \
+    gcc10-c++ \
+    git \
+    make \
+  && rm -rf /var/cache/zypp
+
+RUN update-alternatives --install /usr/bin/cc cc /usr/bin/gcc-10 100
+RUN update-alternatives --install /usr/bin/c++ c++ /usr/bin/g++-10 100