[lldb/test] Fix PExpect.launch issue when disabling color support

This patch should fix a bug in PExpect.launch that happened when color
support is not enabled.

In that case, we need to add the `--no-use-colors` flag to lldb's launch
argument list. However, previously, each character to the string was
appended separately to the `args` list. This patch solves that by adding
the whole string to the list.

This should fix the TestIOHandlerResize failure on GreenDragon.

Differential Revision: https://reviews.llvm.org/D126021



Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>