fix(cicontext): cascade AND-group variables to later members' if: conditions

Variables set by an earlier AND-group member's variables: block are now
injected into the evaluation context before testing later members' if:
expressions. This matches GitLab CI behaviour where e.g. element 0 sets
DEPLOY=true and element 1 can then check $DEPLOY without requiring the
caller to inject that variable manually.

Previously evalRuleGroup passed the same base vars closure to every
member, so cascaded variables were never visible during if: evaluation
(only in the merged output returned after the group fired).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

testdata/nested_rules.yml

@@ -17,6 +17,16 @@ workflow:
       variables:
         PIPELINE_NAME: "deploy"
 
+  # AND-group where element 0 sets PHASE=build; element 1 checks $PHASE (cascade).
+  # Without cascading, element 1 would never match because PHASE is not in
+  # pipeline variables. With cascading, element 1 sees PHASE from element 0.
+  - - if: "$CI_COMMIT_BRANCH"
+      variables:
+        PHASE: build
+    - if: "$PHASE"
+      variables:
+        PIPELINE_NAME: "branch-build"
+
 variables:
   DEPLOY: "false"