CI: Use most recent CrateDB 4.7.1

Author: amotl

.github/workflows/tests.yml

@@ -18,7 +18,7 @@ jobs:
       matrix:
         os: [ubuntu-latest, macos-latest]
         python-version: [3.5, 3.6, 3.7, 3.8, 3.9]
-        cratedb-version: ['4.5.0']
+        cratedb-version: ['4.7.1']
         sqla-version: ['1.1.18', '1.2.19', '1.3.23']
       fail-fast: true