Fix tests by downgrading to grafanalib==0.7.0

grafanalib 0.7.1 and newer no longer supports Python 3.7.

Author: amotl

setup.py

@@ -35,7 +35,7 @@
     "test": [
         "pytest<8",
         "lovely-pytest-docker<1",
-        "grafanalib<0.8",
+        "grafanalib==0.7.0",
     ]
 }