Updated CI to use --disk-cache.

[smolkaj]

Changes

• Use bazel --disk_cache in CI runs.
• Create new Action cache entries more often.
  • Before: Only when hashFiles('**/*_deps.bzl', '**/*.bazelrc') changed.
  • After: As before, and additionally:
  • Always for master-branch builds
  • Always when build took >= 5 minutes.

Motivation

Using --disk_cache has the following advantage [source]:

running bazel build without --disk_cache will result in re-builds if you make changes and change them back, even inside the same directory

Adding new Action cache entries increases the expected relevance ("freshness") of cache hits.

Expected result

Faster CI runs. Reduction in slow CI runs.

Empirical result

The time for a re-run of the bazel CI script with no code changes drops from ~ 2 minutes to < 1 min.

Before

After