Revert "Delete cache"

This reverts commit a142731.

.github/workflows/spark_master_test.yaml

@@ -24,6 +24,19 @@ jobs:
         with:
           distribution: "zulu"
           java-version: "17"
+      - name: Cache Scala, SBT
+        uses: actions/cache@v3
+        with:
+          path: |
+            ~/.sbt
+            ~/.ivy2
+            ~/.cache/coursier
+            !~/.cache/coursier/v1/https/repository.apache.org/content/groups/snapshots
+          # Change the key if dependencies are changed. For each key, GitHub Actions will cache the
+          # the above directories when we use the key for the first time. After that, each run will
+          # just use the cache. The cache is immutable so we need to use a new key when trying to
+          # cache new stuff.
+          key: delta-sbt-cache-spark-master-scala${{ matrix.scala }}
       - name: Install Job dependencies
         run: |
           sudo apt-get update