Fix a bug with cancelling "attach -w" after you have run a process previously (#65822)

The problem is that the when the "attach" command is initiated, the
ExecutionContext for the command has a process - it's the exited one
from the previour run. But the `attach wait` creates a new process for
the attach, and then errors out instead of interrupting when it finds
that its process and the one in the command's ExecutionContext don't
match.

This change checks that if we're returning a target from
GetExecutionContext, we fill the context with it's current process, not
some historical one.