Replace reranker image with dummy in tests

[dirkkul]

Cuts down start time for weaviate in CI by ~1min20sec

[orca-security-eu]

Orca Security Scan Summary

Status	Check	Issues by priority
Passed	Infrastructure as Code	0   0   0   0	View in Orca
Passed	Secrets	0   0   0   0	View in Orca
Passed	Vulnerabilities	0   0   0   0	View in Orca

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.95%. Comparing base (a373ee6) to head (41b77aa).
Report is 174 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1476      +/-   ##
==========================================
- Coverage   93.98%   91.95%   -2.03%     
==========================================
  Files         221      174      -47     
  Lines       21332    14910    -6422     
==========================================
- Hits        20048    13711    -6337     
+ Misses       1284     1199      -85     

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