fix: update template with noop returned undefined template (#11688)

* fix: doing a noop patch to templates resulted in 404

The patch response did not include the template. The UI required the
template to be returned to form the new page path

null is more explicit, and harder to make occur by mistake.

enterprise/coderd/templates_test.go

@@ -687,6 +687,44 @@ func TestTemplates(t *testing.T) {
 		require.Empty(t, template.DeprecationMessage)
 		require.False(t, template.Deprecated)
 	})
+
+	// Create a template, remove the group, see if an owner can
+	// still fetch the template.
+	t.Run("GetOnEveryoneRemove", func(t *testing.T) {
+		t.Parallel()
+		owner, first := coderdenttest.New(t, &coderdenttest.Options{
+			Options: &coderdtest.Options{
+				IncludeProvisionerDaemon: true,
+				TemplateScheduleStore:    schedule.NewEnterpriseTemplateScheduleStore(agplUserQuietHoursScheduleStore()),
+			},
+			LicenseOptions: &coderdenttest.LicenseOptions{
+				Features: license.Features{
+					codersdk.FeatureAccessControl: 1,
+					codersdk.FeatureTemplateRBAC:  1,
+				},
+			},
+		})
+
+		client, _ := coderdtest.CreateAnotherUser(t, owner, first.OrganizationID, rbac.RoleTemplateAdmin())
+		version := coderdtest.CreateTemplateVersion(t, client, first.OrganizationID, nil)
+		template := coderdtest.CreateTemplate(t, client, first.OrganizationID, version.ID)
+
+		ctx := testutil.Context(t, testutil.WaitMedium)
+		err := client.UpdateTemplateACL(ctx, template.ID, codersdk.UpdateTemplateACL{
+			UserPerms: nil,
+			GroupPerms: map[string]codersdk.TemplateRole{
+				// OrgID is the everyone ID
+				first.OrganizationID.String(): codersdk.TemplateRoleDeleted,
+			},
+		})
+		require.NoError(t, err)
+
+		ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitLong)
+		defer cancel()
+
+		_, err = owner.Template(ctx, template.ID)
+		require.NoError(t, err)
+	})
 }
 
 func TestTemplateACL(t *testing.T) {