Fix validation error for ImagePullPolicy in charms

Change-Id: I00711202fdbacd73e9205dd3fc34424893440be5
Signed-off-by: sousaedu <eduardo.sousa@canonical.com>
diff --git a/installers/charm/pol/src/charm.py b/installers/charm/pol/src/charm.py
index d1341c1..36eb8c6 100755
--- a/installers/charm/pol/src/charm.py
+++ b/installers/charm/pol/src/charm.py
@@ -49,7 +49,7 @@
     log_level: str
     mongodb_uri: Optional[str]
     mysql_uri: Optional[str]
-    image_pull_policy: Optional[str]
+    image_pull_policy: str
 
     @validator("log_level")
     def validate_log_level(cls, v):