Storage Class don´t use global.storageClass (#601) (#602)

### Description of the change

The code change ensures proper usage of gitea.persistence.storageClass, improving configuration accuracy and code readability.

### Applicable issues

  - fixes #601

Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/602
Reviewed-by: pat-s <pat-s@noreply.gitea.com>
Co-authored-by: florianspk <florianspk@gmail.com>
Co-committed-by: florianspk <florianspk@gmail.com>

unittests/deployment/storage-class-configuration.yaml

@@ -0,0 +1,39 @@
+# File: tests/gitea-storageclass-tests.yaml
+
+suite: storage class configuration tests
+
+release:
+  name: gitea-storageclass-tests
+  namespace: testing
+
+templates:
+  - templates/gitea/pvc.yaml
+
+tests:
+  - it: should set storageClassName when persistence.storageClass is defined
+    template: templates/gitea/pvc.yaml
+    set:
+      persistence.storageClass: "my-storage-class"
+    asserts:
+      - equal:
+          path: "spec.storageClassName"
+          value: "my-storage-class"
+
+  - it: should set global.storageClass when persistence.storageClass is not defined
+    template: templates/gitea/pvc.yaml
+    set:
+      global.storageClass: "default-storage-class"
+    asserts:
+      - equal:
+          path: spec.storageClassName
+          value: "default-storage-class"
+
+  - it: should set storageClassName when persistence.storageClass is defined and global.storageClass is defined
+    template: templates/gitea/pvc.yaml
+    set:
+      global.storageClass: "default-storage-class"
+      persistence.storageClass: "my-storage-class"
+    asserts:
+      - equal:
+          path: spec.storageClassName
+          value: "my-storage-class"