docs(gfql): mark illustrative benchmark_graphframes snippets doc-test:skip

The two GFQL/GraphFrames code blocks are illustrative (reference an undefined
g/gf/seeds and engine="polars"), so the doc-example runner was executing them
and failing test-docs. Mark both with '.. doc-test: skip' — they are shown for
reading, not execution. Removes this page's contribution to the test-docs
failure on #1668.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: lmeyerov

docs/source/gfql/benchmark_graphframes.rst

@@ -113,6 +113,8 @@ graphs carry no attributes, so ``degree`` is precomputed at cold-load (charged
 to load, not to the query, for *both* systems) and used as the natural
 threshold column.
 
+.. doc-test: skip
+
 .. code-block:: python
 
    # GFQL
@@ -133,6 +135,8 @@ trivial on both.
 
 Undirected 1-hop expansion from a fixed 50-node high-degree seed set.
 
+.. doc-test: skip
+
 .. code-block:: python
 
    # GFQL