Fix python 3.11 compatibility am: 58c5a33bda am: 9b18ec1e49 am: e88f1b5c92 am: f0793e920b

Original change: https://android-review.googlesource.com/c/platform/external/nanopb-c/+/2726973

Change-Id: Ic767d2dd83fd766ac9e2497168da67cf65d3c953
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>
diff --git a/generator/nanopb_generator.py b/generator/nanopb_generator.py
index b4f1d83..d145dd3 100755
--- a/generator/nanopb_generator.py
+++ b/generator/nanopb_generator.py
@@ -1641,7 +1641,7 @@
             optfilename = os.path.join(p, optfilename)
             if options.verbose:
                 sys.stderr.write('Reading options from ' + optfilename + '\n')
-            Globals.separate_options = read_options_file(open(optfilename, "rU"))
+            Globals.separate_options = read_options_file(open(optfilename, 'r', encoding = 'utf-8'))
             break
     else:
         # If we are given a full filename and it does not exist, give an error.