[FIX] project: allow edit priority task in project sharing

Before this commit, the `priority` field in task was in readonly in
project sharing feature.

This commit allows the `priority` field in task be edited by a portal
user in project sharing.

task-2633229

closes #77156

X-original-commit: 62572e17d6cd62f16287d530c247dbe9b8501e0c

addons/project/models/project.py

@@ -38,7 +38,6 @@ PROJECT_TASK_READABLE_FIELDS = {
     'company_id',
     'displayed_image_id',
     'display_name',
-    'priority',
     'portal_user_names',
 }
 
@@ -54,6 +53,7 @@ PROJECT_TASK_WRITABLE_FIELDS = {
     'kanban_state',
     'child_ids',
     'parent_id',
+    'priority',
 }
 
 class ProjectTaskType(models.Model):