Add the g/um as a supported Si unit

Author: Gorshanov Vadim

src/tikzplotlib/_axes.py

@@ -21,6 +21,7 @@ def _siunitx_texification(string: str) -> str:
     string = re.sub(r"\shour", r" \\si{\\hour}", string)
     string = re.sub(r"\scc", r" \\si{\\cc}", string)
     string = re.sub(r"\s\\%", r" \\si{\\percent}", string)
+    string = re.sub(r"\sg/um", r" \\si{\\g\\per\\um}", string)
     return string