releasetools: Fix releasetools_py3_test.

Test: Use a lunch'd target;
      `atest --host releasetools_test releasetools_py3_test`
Change-Id: Ibcced83a7989ef8fc15464728ab1d5fa71ca988e
diff --git a/tools/releasetools/test_ota_from_target_files.py b/tools/releasetools/test_ota_from_target_files.py
index 9825a5e..f7d59da 100644
--- a/tools/releasetools/test_ota_from_target_files.py
+++ b/tools/releasetools/test_ota_from_target_files.py
@@ -596,7 +596,7 @@
 
     with zipfile.ZipFile(target_file) as verify_zip:
       namelist = verify_zip.namelist()
-      ab_partitions = verify_zip.read('META/ab_partitions.txt')
+      ab_partitions = verify_zip.read('META/ab_partitions.txt').decode()
 
     self.assertIn('META/ab_partitions.txt', namelist)
     self.assertIn('IMAGES/system.img', namelist)
@@ -676,9 +676,9 @@
 
     with zipfile.ZipFile(target_file) as verify_zip:
       namelist = verify_zip.namelist()
-      updated_misc_info = verify_zip.read('META/misc_info.txt')
+      updated_misc_info = verify_zip.read('META/misc_info.txt').decode()
       updated_dynamic_partitions_info = verify_zip.read(
-          'META/dynamic_partitions_info.txt')
+          'META/dynamic_partitions_info.txt').decode()
 
     self.assertIn('META/ab_partitions.txt', namelist)
     self.assertIn('IMAGES/system.img', namelist)