Add new nondeterministic_devhelp_documentation_generated_by_gtk_doc toolchain issue.

issues.yml

@@ -2047,3 +2047,7 @@ nondeterministic_output_in_code_generated_by_ros_genpy:
     python3-rosgenpy generates Python code to serialise/deserialise messages in
     a similar way to Protocol Buffers. However, the code itself is not
     determinstic in various orderings, etc.
+nondeterministic_devhelp_documentation_generated_by_gtk_doc:
+  description: |
+    gtk-doc can generate .devhelp2 files (or similar) with non-deterministic
+    headers such as "Index of new API in 1.2.3".