Fix incorrect string operations on bytes output of subprocess causing…

… wrong shell type to be selected (AcademySoftwareFoundation#1765)

Signed-off-by: Parikshit Tiwari <parikshitatiwari@gmail.com>
Signed-off-by: Jean-Christophe Morin <jean_christophe_morin@hotmail.com>
Co-authored-by: Jean-Christophe Morin <jean_christophe_morin@hotmail.com>

src/rez/system.py

@@ -86,7 +86,7 @@ def shell(self):
                 # print an error message: "process ID out of range".
                 try:
                     args = ['ps', '-o', 'args=', '-p', str(parent_pid)]
-                    proc = sp.Popen(args, stdout=sp.PIPE)
+                    proc = sp.Popen(args, stdout=sp.PIPE, text=True)
                     output = proc.communicate()[0]
                     shell = os.path.basename(output.strip().split()[0]).replace('-', '')
                 except Exception: