Bug 1638977 - Convert 'mach prettier-format' to run with Python 3, r=sylvestre

Differential Revision: https://phabricator.services.mozilla.com/D93350

mach

@@ -21,7 +21,6 @@ py2commands="
     marionette-test
     jstests
     mozharness
-    prettier-format
     raptor
     raptor-test
     telemetry-tests-client

python/mozbuild/mozbuild/code_analysis/mach_commands.py

@@ -2060,7 +2060,7 @@ class StaticAnalysis(MachCommandBase):
         args = [binary, prettier, "--stdin-filepath", assume_filename]
 
         process = subprocess.Popen(args, stdin=subprocess.PIPE)
-        with open(path, "r") as fin:
+        with open(path, "rb") as fin:
             process.stdin.write(fin.read())
             process.stdin.close()
             process.wait()