make the error message readable (Lightning-AI#2729)

* make the error message readable

make the error message readable by adding spaces, fixing a type "his -> this",

* cleanup

* Update pytorch_lightning/trainer/auto_mix_precision.py

* Apply suggestions from code review

Co-authored-by: Ethan Harris <ewah1g13@soton.ac.uk>

Co-authored-by: Jirka Borovec <Borda@users.noreply.github.com>
Co-authored-by: Ethan Harris <ewah1g13@soton.ac.uk>

Author: 3 people

pytorch_lightning/trainer/auto_mix_precision.py

@@ -25,8 +25,9 @@ def init_amp(self):
         if self.use_amp and not APEX_AVAILABLE:  # pragma: no-cover
             raise ModuleNotFoundError(
                 "You set `use_amp=True` but do not have apex installed."
-                "Install apex first using this guide and rerun with use_amp=True:"
-                "https://github.com/NVIDIA/apex#linux his run will NOT use 16 bit precision"
+                " Install apex first using this guide: https://github.com/NVIDIA/apex#linux"
+                " and rerun with `use_amp=True`."
+                " This run will NOT use 16 bit precision."
             )
 
         if self.use_amp: