Added disk space check command after cache restore

Added a step printing disk space after the cache is restored. We had
problems with executor running out of space. With this step we can debug
disk usage after the cache is restored. We assume that available disk
space for `/` before cache restore to be at ~20 GB.

.github/workflows/client.yml

@@ -15,6 +15,13 @@ jobs:
       - uses: actions/checkout@v2
       - uses: satackey/[email protected]
         continue-on-error: true # ignore the failure of a step and avoid terminating the job
+      # TODO: This step was left here intentionally so we can track disk space
+      # usage for a while. We were trying to fight problems with out of disk space
+      # that happened due to the size of data restored from cache. The cache size
+      # was growing linearly with subsequent workflow runs. We want to observe
+      # available disk space for `/`. Fresh execution starts with 20 GB, we expect
+      # to have no less than 15 GB after the cache is restored.
+      - run: sudo df -h
       - name: Run Docker build
         run: |
           docker build \