Bump Python version to 3.8 in TensorFlow v1 workflow

Signed-off-by: Beat Buesser <[email protected]>

Author: Beat Buesser

.github/workflows/ci-tensorflow-v1.yml

@@ -25,9 +25,9 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - name: TensorFlow 1.15.5 (Keras 2.2.5 Python 3.7)
+          - name: TensorFlow 1.15.5 (Keras 2.2.5 Python 3.8)
             framework: tensorflow
-            python: 3.7
+            python: 3.8
             tensorflow: 1.15.5
             tf_version: v1
             keras: 2.2.5