[Docs] Update snapshot-too-old-when-running-ysql-dump documentation.

[rthallamko3]

Description

Update the workaround for the following error - Snapshot too old error message - The master flag needs to be changed and not the tserver.

If you really need to use ysql_dump, you can increase the [--timestamp_history_retention_interval_sec](https://docs.yugabyte.com/preview/reference/configuration/yb-tserver/#timestamp-history-retention-interval-sec) gflag in YB-TServer and retry.

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[rthallamko3]

Documentation change has landed.