fix(redis): default sentinel ports per address

[haoshengzhen]

Summary

When parsing redis+sentinel URLs with multiple sentinel addresses, an address without an explicit port used the full URL host list as its host fallback. For example:

redis+sentinel://sentinel-1,sentinel-2:26379/master

could produce an invalid first address instead of defaulting only sentinel-1 to port 6379.

This change applies the missing-port fallback per sentinel address, preserving explicitly configured ports on the other addresses. It also adds a regression test and a changelog fragment.

Testing

• gofmt
• git diff --check
• Temporary Go reproduction confirming the old address parsing logic fails for mixed explicit/default sentinel ports, while the new logic returns sentinel-1:6379 and sentinel-2:26379.

[CLAassistant]

All committers have signed the CLA.

[haoshengzhen]

@bragaigor Hi, Could you please review this PR at your convenience? Thank you very much.