Clarify pressure parameter description in qha.py

The units weren't mentioned. I presume it is GPa but would always appreciate a sanity check.

Author: Andrew-S-Rosen

src/atomate2/common/flows/qha.py

@@ -63,7 +63,7 @@ class CommonQhaMaker(Maker, ABC):
     t_max: float | None
         Maximum temperature until which the QHA will be performed
     pressure: float | None
-        Pressure at which the QHA will be performed (default None, no pressure)
+        Pressure (GPa) at which the QHA will be performed (default None, no pressure)
     skip_analysis: bool
         Skips the analysis step and only performs EOS and phonon computations.
     ignore_imaginary_modes: bool