ci: fix the usage of unstable container skip (#2001)

Co-authored-by: pyansys-ci-bot <[email protected]>

Author: RobPasMue

.github/workflows/ci_cd.yml

@@ -181,7 +181,7 @@ jobs:
             exit 1
           }
 
-          $A = $env:SKIP_UNSTABLE_CONTAINERS_TEMPORARILY -eq 1
+          $A = ${{ vars.SKIP_UNSTABLE_CONTAINERS_TEMPORARILY }} -eq 1
           $B = $ImagesAreEqual -eq 1
 
           # Calculate the logical expression
@@ -386,7 +386,7 @@ jobs:
             exit 1
           fi
 
-          A=$([[ "$SKIP_UNSTABLE_CONTAINERS_TEMPORARILY" == "1" ]] && echo true || echo false)
+          A=$([[ "${{ vars.SKIP_UNSTABLE_CONTAINERS_TEMPORARILY }}" == "1" ]] && echo true || echo false)
           B=$([[ "$ImagesAreEqual" == "1" ]] && echo true || echo false)
 
           # Calculate the logical expression

doc/changelog.d/2001.maintenance.md

@@ -0,0 +1 @@
+fix the usage of unstable container skip