Add caching to CI jobs (#13712)

- Seems to be improving times for shorter jobs at least.

- Remove Go 1.16.x tests for IAM and replication

.github/workflows/iam-integrations.yaml

@@ -50,7 +50,7 @@ jobs:
       # are turned off - i.e. if ldap="", then ldap server is not enabled for
       # the tests.
       matrix:
-        go-version: [1.16.x, 1.17.x]
+        go-version: [1.17.x]
         ldap: ["", "localhost:389"]
         etcd: ["", "http://localhost:2379"]
         openid: ["", "http://127.0.0.1:5556/dex"]
@@ -68,7 +68,15 @@ jobs:
       - uses: actions/setup-go@v2
         with:
           go-version: ${{ matrix.go-version }}
-      - name: Test LDAP/OpenID with Etcd combo
+      - uses: actions/cache@v2
+        with:
+          path: |
+            ~/.cache/go-build
+            ~/go/pkg/mod
+          key: ${{ runner.os }}-${{ matrix.go-version }}-go-${{ hashFiles('**/go.sum') }}
+          restore-keys: |
+            ${{ runner.os }}-${{ matrix.go-version }}-go-
+      - name: Test LDAP/OpenID/Etcd combo
         env:
           LDAP_TEST_SERVER: ${{ matrix.ldap }}
           ETCD_SERVER: ${{ matrix.etcd }}