.Net: minor change so that inputs are not skipped in Planner example

[nkelly75]

Description

While learning Semantic Kernel (and having already run various other tests successfully) I wanted to try out the Planner example (described here). I added some sample inputs to SimulatedInputText. I then noticed that the chat loop was effectively skipping every second input due to a double call to ReadLine(). If there was an odd number of inputs we saw a failure due to the last ReadLine() returning null

The simple fix replaces the second ReadLine() call with the userInput variable from the first call.

Note: for illustration purposes, the PR includes my sample inputs commented out. These can be removed if necessary for approval.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄