test(fractional): add invalid/missing variant fallback cases

Per review feedback: add two rows to the nested-var scenario that
exercise fallback behavior when the resolved variant name is not
present in the flag's variants map.

  | jon@company.com | yellow | fallback |  (variant not in map → error → caller default)
  | jon@company.com |        | fallback |  (empty string → not in map → error → caller default)

Signed-off-by: Simon Schrottner <simon.schrottner@dynatrace.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: aepfli

gherkin/targeting.feature

@@ -101,10 +101,12 @@ Feature: Targeting rules
     When the flag was evaluated with details
     Then the resolved details value should be "<value>"
     Examples:
-      | targetingKey    | color | value |
-      | jon@company.com | red   | red   |
-      | jon@company.com | green | green |
-      | user1           | red   | blue  |
+      | targetingKey    | color  | value    |
+      | jon@company.com | red    | red      |
+      | jon@company.com | green  | green    |
+      | user1           | red    | blue     |
+      | jon@company.com | yellow | fallback |
+      | jon@company.com |        | fallback |
 
   @string
   Scenario Outline: Substring operators