Fixes wrong target syntax

Author: spjuhel

doc/development/Guide_test_fixtures.ipynb

@@ -5,7 +5,7 @@
    "id": "359d0d32-68c5-4e8d-8b34-2c5b2a0cad21",
    "metadata": {},
    "source": [
-    "{#fixture-tutorial}\n",
+    "(fixture-tutorial)=\n",
     "# Testing with pytest Fixtures\n",
     "\n",
     "**Fixtures** are pytest's way of setting up the data and objects that tests need. Think of them as reusable \"preparation steps\" that run before your tests.\n",