.github/workflows: Bump Bazel for testing to 5.0.0 (#123)

Now you can run locally using the version of your choice.

.github/workflows/testing.yml

@@ -1,26 +1,22 @@
-# This is a basic workflow to help you get started with Actions
-
 name: Testing
 
-# Controls when the action will run. 
 on:
   push:
   pull_request:
 
 permissions:
   contents: read
 
-# A workflow run is made up of one or more jobs that can run sequentially or in parallel
+env:
+  USE_BAZEL_VERSION: 5.0.0
+
 jobs:
-  # This workflow contains a single job called "build"
   test:
-    # The type of runner that the job will run on
     runs-on: ubuntu-latest
 
-    # Steps represent a sequence of tasks that will be executed as part of the job
     steps:
       - name: Checkout repo
         uses: actions/checkout@v2
 
       - name: Run bazel build
-        run: ./tools/bazel build //...
+        run: bazelisk build //...