Fix the out of boundary error

.changelog/9628.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+monitoring: fixed the index out of range crash in `dashboard_json` perma-diffs for the resource `google_monitoring_dashboard`
+```

google/services/monitoring/resource_monitoring_dashboard.go

@@ -33,7 +33,7 @@ func removeComputedKeys(old map[string]interface{}, new map[string]interface{})
 
 		if reflect.ValueOf(v).Kind() == reflect.Slice {
 			for i, j := range v.([]interface{}) {
-				if reflect.ValueOf(j).Kind() == reflect.Map {
+				if reflect.ValueOf(j).Kind() == reflect.Map && len(new[k].([]interface{})) > i {
 					old[k].([]interface{})[i] = removeComputedKeys(j.(map[string]interface{}), new[k].([]interface{})[i].(map[string]interface{}))
 				}
 			}

google/services/monitoring/resource_monitoring_dashboard_test.go

@@ -119,6 +119,15 @@ func TestAccMonitoringDashboard_update(t *testing.T) {
 				ImportStateVerify:       true,
 				ImportStateVerifyIgnore: []string{"project"},
 			},
+			{
+				Config: testAccMonitoringDashboard_gridLayoutUpdate(),
+			},
+			{
+				ResourceName:            "google_monitoring_dashboard.dashboard",
+				ImportState:             true,
+				ImportStateVerify:       true,
+				ImportStateVerifyIgnore: []string{"project"},
+			},
 		},
 	})
 }
@@ -244,6 +253,52 @@ EOF
 `)
 }
 
+func testAccMonitoringDashboard_gridLayoutUpdate() string {
+	return fmt.Sprintf(`
+resource "google_monitoring_dashboard" "dashboard" {
+  dashboard_json = <<EOF
+{
+  "displayName": "Grid Layout Example",
+  "gridLayout": {
+    "columns": "2",
+    "widgets": [
+      {
+        "title": "Widget 1",
+        "xyChart": {
+          "dataSets": [{
+            "timeSeriesQuery": {
+              "timeSeriesFilter": {
+                "filter": "metric.type=\"agent.googleapis.com/nginx/connections/accepted_count\"",
+                "aggregation": {
+                  "perSeriesAligner": "ALIGN_RATE"
+                }
+              },
+              "unitOverride": "1"
+            },
+            "plotType": "LINE"
+          }],
+          "timeshiftDuration": "0s",
+          "yAxis": {
+            "label": "y1Axis",
+            "scale": "LINEAR"
+          }
+        }
+      },
+      {
+        "text": {
+          "content": "Widget 2",
+          "format": "MARKDOWN"
+        }
+      }
+    ]
+  }
+}
+
+EOF
+}
+`)
+}
+
 func testAccMonitoringDashboard_rowLayout() string {
 	return fmt.Sprintf(`
 resource "google_monitoring_dashboard" "dashboard" {