In github workflow, use bazel caching

.bazelignore

@@ -7,3 +7,6 @@ bazel-testlogs
 
 # Github
 .github
+
+# postgres mounts
+postgres-data

.github/workflows/ci.bazelrc

@@ -1,8 +1,7 @@
 # Bazel settings to apply on CI only
 # Included with a --bazelrc option in the call to bazel
 build --announce_rc
-test --test_output=errors
 build --disk_cache=$HOME/.cache/bazel
 build --repository_cache=$HOME/.cache/bazel-repo
-# For bazel-in-bazel testing
-test --test_env=XDG_CACHE_HOME
+
+test --test_output=errors

.github/workflows/main.yml

@@ -10,10 +10,26 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
+      # Caches and restores the bazelisk download directory, the bazel build directory.
+      - name: Cache bazel
+        uses: actions/cache@v4
+        env:
+          cache-name: bazel-cache
+        with:
+          path: |
+            ~/.cache/bazelisk
+            ~/.cache/bazel
+            ~/.cache/bazel-repo
+          key: ${{ runner.os }}-${{ env.cache-name }}-${{ github.ref }}-${{ github.sha }}
+          # Pull caches from:
+          # - The current sha,
+          # - The current branch,
+          # - base branch
+          restore-keys: |
+            ${{ runner.os }}-${{ env.cache-name }}-${{ github.ref }}-${{ github.sha }}
+            ${{ runner.os }}-${{ env.cache-name }}-${{ github.ref }}-
+            ${{ runner.os }}-${{ env.cache-name }}-${{ github.base_ref }}-
       - name: Checkout
         uses: actions/checkout@v4
       - name: bazel test //...
-        env:
-          # Bazelisk will download bazel to here
-          XDG_CACHE_HOME: ~/.cache/bazel-repo
         run: bazel --bazelrc=.github/workflows/ci.bazelrc --bazelrc=.bazelrc test //...