fix(api): issue state change is not idempotent

The PATCH if issue & pull request switched to use the service
functions instead. However, the service function changing the state is
not idempotent. Instead of doing nothing which changing from open to
open or close to close, it will fail with an error like:

 Issue [2472] 0 was already closed

Regression of: 6a4bc0289d

Fixes: https://codeberg.org/forgejo/forgejo/issues/4686
(cherry picked from commit e9e3b8c0f3)

tests/integration/api_issue_test.go

@@ -215,6 +215,21 @@ func TestAPIEditIssue(t *testing.T) {
 	assert.Equal(t, int64(0), int64(issueAfter.DeadlineUnix))
 	assert.Equal(t, body, issueAfter.Content)
 	assert.Equal(t, title, issueAfter.Title)
+
+	// verify the idempotency of state, milestone, body and title changes
+	req = NewRequestWithJSON(t, "PATCH", urlStr, api.EditIssueOption{
+		State:     &issueState,
+		Milestone: &milestone,
+		Body:      &body,
+		Title:     title,
+	}).AddTokenAuth(token)
+	resp = MakeRequest(t, req, http.StatusCreated)
+	var apiIssueIdempotent api.Issue
+	DecodeJSON(t, resp, &apiIssueIdempotent)
+	assert.Equal(t, apiIssue.State, apiIssueIdempotent.State)
+	assert.Equal(t, apiIssue.Milestone.Title, apiIssueIdempotent.Milestone.Title)
+	assert.Equal(t, apiIssue.Body, apiIssueIdempotent.Body)
+	assert.Equal(t, apiIssue.Title, apiIssueIdempotent.Title)
 }
 
 func TestAPIEditIssueAutoDate(t *testing.T) {