fix: prevent RuntimeError in asyncio.cluster.NodesManager.initialize()

[jakob-keller]

Pull Request check-list

• Do tests and lints pass with this change?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?

Description of change

The change prevents RuntimeError being raised when valkey.asyncio.cluster.NodeManager.startup_nodes are modified while performing .initialize().

Fixes #181

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.17%. Comparing base (f6065c8) to head (77f3519).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #184   +/-   ##
=======================================
  Coverage   76.17%   76.17%           
=======================================
  Files         130      130           
  Lines       33980    33980           
=======================================
+ Hits        25883    25885    +2     
+ Misses       8097     8095    -2     

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[ahmedsobeh]

LGTM, thanks for the PR

[mkmkme]

The CI failure seems unrelated. I'll fix it promptly and rebase the PR on the top of the current main

[mkmkme]

The CI is broken due to the bug in valkey 8.1: valkey-io/valkey#2035

I'll restart the tests when the bug is fixed.