Add a pytest mark for system tests that require Internet connection

We skip those by default as:

a) we don't want to stress the upstream servers in every CI pipeline
b) system tests need to be runnable in a isolated environment by default

.gitlab-ci.yml

@@ -263,10 +263,13 @@ stages:
   rules:
     - if: '$CI_PIPELINE_SOURCE =~ /^(api|pipeline|schedule|trigger|web)$/'
 
+.default-triggering-rules_list: &default_triggering_rules_list
+  - if: '$CI_PIPELINE_SOURCE =~ /^(api|merge_request_event|pipeline|schedule|trigger|web)$/'
+  - if: '$CI_COMMIT_TAG != null'
+
 .default-triggering-rules: &default_triggering_rules
   rules:
-    - if: '$CI_PIPELINE_SOURCE =~ /^(api|merge_request_event|pipeline|schedule|trigger|web)$/'
-    - if: '$CI_COMMIT_TAG != null'
+    - *default_triggering_rules_list
 
 .precheck: &precheck_job
   <<: *default_triggering_rules
@@ -918,6 +921,11 @@ system:gcc:bookworm:amd64:
   needs:  # using artifacts from unit test job is required for gcov
     - job: unit:gcc:bookworm:amd64
       artifacts: true
+  rules:
+    - if: '$CI_PIPELINE_SOURCE == "schedule"'
+      variables:
+        CI_ENABLE_LIVE_INTERENT_TESTS: 1
+    - *default_triggering_rules_list
 
 unit:gcc:bookworm:amd64:
   <<: *debian_bookworm_amd64_image

bin/tests/system/isctest/mark.py

@@ -22,6 +22,11 @@ long_test = pytest.mark.skipif(
     not os.environ.get("CI_ENABLE_LONG_TESTS"), reason="CI_ENABLE_LONG_TESTS not set"
 )
 
+live_internet_test = pytest.mark.skipif(
+    not os.environ.get("CI_ENABLE_LIVE_INTERNET_TESTS"),
+    reason="CI_ENABLE_LIVE_INTERNET_TESTS not set",
+)
+
 
 def feature_test(feature):
     feature_test_bin = os.environ["FEATURETEST"]