Allow replica to master promotion in nodes_cache

[zakaf]

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Description of change

Please provide a description of the change here.
fixes #2433

When replica is promoted to master, ClusterNode's server_type must change accordingly, but the current implementation reuses the server_type, so no master is found in nodes_cache after initialization

This PR changes the server_type to a correct value, even if we reuse ClusterNode from nodes_cache

I've personally experienced this scenario, when i changed instance type in AWS Elasticache

• changing instance type resulted in the addition of a new replica node and that node getting promoted to master

[codecov-commenter]

Codecov Report

Base: 92.24% // Head: 92.22% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (af47499) compared to base (f46d7f3).
Patch coverage: 85.18% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2549      +/-   ##
==========================================
- Coverage   92.24%   92.22%   -0.02%     
==========================================
  Files         115      115              
  Lines       29554    29581      +27     
==========================================
+ Hits        27262    27281      +19     
- Misses       2292     2300       +8     

Impacted Files	Coverage Δ
tests/test_cluster.py	96.83% <84.00%> (-0.29%)	⬇️
redis/cluster.py	90.37% <100.00%> (+0.02%)	⬆️
tests/test_asyncio/test_search.py	98.29% <0.00%> (-0.35%)	⬇️

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