Fix finding spectral gap with identical diffs

[sebimarkgraf]

Issue/s resolved: #715

Changes proposed:

• Change to argmax to prevent multiple identical diffs crashing the algorithm

Type of change

• Bug fix (non-breaking change which fixes an issue)

Due Diligence

• All split configurations tested (tested in test_spectral already)
• Multiple dtypes tested in relevant functions (tested in test_spectral already)
• Updated changelog.md under the title "Pending Additions"

Does this change modify the behaviour of other functions? If so, which?

no

[mtar]

GPU cluster tests are currently disabled on this Pull Request.

[mtar]

GPU cluster tests are currently disabled on this Pull Request.

[mtar]

GPU cluster tests are currently disabled on this Pull Request.

[codecov]

Codecov Report

Merging #716 (68999bb) into master (34c356b) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #716   +/-   ##
=======================================
  Coverage   95.97%   95.97%           
=======================================
  Files          63       63           
  Lines        8056     8056           
=======================================
  Hits         7732     7732           
  Misses        324      324           

Flag	Coverage Δ
gpu	95.08% <100.00%> (+0.16%)	⬆️
unit	94.18% <100.00%> (-0.17%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
heat/cluster/spectral.py	93.44% <100.00%> (ø)

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[coquelin77]

run tests

[mtar]

test this once