Reduce flakiness in TestShardReplicationPositions

[ajm188]

Description

In CI, sometimes 10ms is exhausted simply in context switching, so we end up timing out the request before calling GetTabletMapByShard, rather than in the tabletmanager RPCs we are trying to have timeout.

Bumping the timeout by 10x to try to reduce flakiness.

Related Issue(s)

Fixes #14707.

Checklist

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[vitess-bot]

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[mattlord]

IMO it's probably worth going even higher since I've seen 1+ second pauses (CPU stalls) when SSH'd into the runners in the past. But 10x should definitely help.

[ajm188]

let me bump it a bit further then!