Typo in statistical_ensemble_test/single_run.py

### Brief summary of bug

There seems to by a typo in statistical_ensemble_test/single_run.py:

https://github.com/ESCOMP/CESM/blob/7d3d630b8333db89fa6b22cb91599d914857ecd2/tools/statistical_ensemble_test/single_run.py#L384

This should be `text.` imho

### General bug information

**CESM version you are using:** [Output of `git describe`]

**Machine you are using:** [Fill this in]

**Have you modified the code? (If so, please point us to you changes.):** [Yes / No]

### Details of bug

This is my first bug report for CESM so be patient with me please. I hope I provided all the required information since this seems to be quite straight forward otherwise please let me know.