Skip untestable cells in nbval

Author: vidartf

examples/Animation.ipynb

@@ -288,7 +288,11 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {},
+   "metadata": {
+    "tags": [
+     "nbval-skip"
+    ]
+   },
    "outputs": [],
    "source": [
     "import numpy as np\n",
@@ -315,7 +319,11 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {},
+   "metadata": {
+    "tags": [
+     "nbval-skip"
+    ]
+   },
    "outputs": [],
    "source": [
     "pill_track = NumberKeyframeTrack(name='.morphTargetInfluences[0]', times=[0, 1.5, 3], values=[0, 2.5, 0])\n",
@@ -326,7 +334,11 @@
   {
    "cell_type": "code",
    "execution_count": null,
-   "metadata": {},
+   "metadata": {
+    "tags": [
+     "nbval-skip"
+    ]
+   },
    "outputs": [],
    "source": [
     "camera3 = PerspectiveCamera( position=[5, 3, 5], aspect=view_width/view_height)\n",