Decrease graphviz visualization test size to speed up tests

[mtreinish]

With recent graphviz releases the graphviz_draw() visualization tests for 50 node random graphs were taking an inordinate amount of time. This didn't seem to be an issue in CI but on my local system with graphviz 10.0.1 the time for graphviz to generate a visualization for the 50 node random graph was orders of magnitude slower than the rest of the tests in the rustworkx python tests. This commit decreases the graph size to only be 10 nodes, which reduces the runtime of these tests to be inline with expectations.

[coveralls]

Pull Request Test Coverage Report for Build 8512442232

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 6 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.03%) to 96.503%

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Files with Coverage Reduction	New Missed Lines	%
src/shortest_path/all_pairs_bellman_ford.rs	6	95.53%

Totals
Change from base Build 8470915706:	-0.03%
Covered Lines:	17136
Relevant Lines:	17757

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💛 - Coveralls

[IvanIsCoding]

I agree, as long as we cover all the lines we should be fine.