Use array as default extraEnvs (#18341)

Signed-off-by: Daniel Reigada <daniel@codacy.com>

stable/postgresql/Chart.yaml

@@ -1,6 +1,6 @@
 apiVersion: v1
 name: postgresql
-version: 6.5.5
+version: 6.5.6
 appVersion: 11.5.0
 description: Chart for PostgreSQL, an object-relational database management system (ORDBMS) with an emphasis on extensibility and on standards-compliance.
 keywords:

stable/postgresql/values-production.yaml

@@ -385,4 +385,4 @@ metrics:
     successThreshold: 1
 
 # Define custom environment variables to pass to the image here
-extraEnv: {}
+extraEnv: []

stable/postgresql/values.yaml

@@ -385,4 +385,4 @@ metrics:
     successThreshold: 1
 
 # Define custom environment variables to pass to the image here
-extraEnv: {}
+extraEnv: []