fix BIRCH intercluster distance

[andiwg]

Use the correct value for Inter-Cluster distance in BIRCH:

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 52.40%. Comparing base (550de99) to head (ebe6d47).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ula/distance/BIRCHAverageInterclusterDistance.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #116      +/-   ##
============================================
- Coverage     52.41%   52.40%   -0.01%     
+ Complexity    12833    12832       -1     
============================================
  Files          1846     1846              
  Lines         93979    93979              
  Branches      17468    17468              
============================================
- Hits          49256    49252       -4     
- Misses        40397    40399       +2     
- Partials       4326     4328       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.