Item graph display too many items

[BenjaminCharmes]

Closes #1355

Test from #1360 work with this fix (local at least)

[cypress]

datalab    Run #3921

Run Properties:   Passed #3921  •  3639d0a6f1 ℹ️: Merge 895719370f8b2dd4d5f2f6dd348eea8948953ee2 into b121182e7a2c4ca1eebd268ed0b8...

Project	datalab
Branch Review	bc/slow-itemgraph
Run status	Passed #3921
Run duration	06m 54s
Commit	3639d0a6f1 ℹ️: Merge 895719370f8b2dd4d5f2f6dd348eea8948953ee2 into b121182e7a2c4ca1eebd268ed0b8...
Committer	Ben Charmes
View all properties for this run ↗︎

---

Test results
Failures	0
Flaky	0
Pending	0
Skipped	0
Passing	336
View all changes introduced in this branch ↗︎

[codecov]

Codecov Report

❌ Patch coverage is 95.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 80.38%. Comparing base (767e66d) to head (8957193).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
pydatalab/src/pydatalab/routes/v0_1/graphs.py	95.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1367      +/-   ##
==========================================
+ Coverage   80.06%   80.38%   +0.31%     
==========================================
  Files          70       70              
  Lines        4731     4767      +36     
==========================================
+ Hits         3788     3832      +44     
+ Misses        943      935       -8     

Files with missing lines	Coverage Δ
pydatalab/src/pydatalab/routes/v0_1/graphs.py	94.80% <95.00%> (+17.88%)	⬆️

... and 1 file with indirect coverage changes

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