gopls/integration/govim: fix govim tests without a go.mod file

govim tests without a go.mod file were accidentally picking up the
go.mod file from the build context at /workspace/go.mod.

To fix this, run govim tests in a new, dedicated artifacts volume
mounted at /artifacts.

Change-Id: Ie224bbb730741d047be26a6d057a023ddc8a3453
Reviewed-on: https://go-review.googlesource.com/c/tools/+/226157
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
diff --git a/gopls/integration/govim/cloudbuild.yaml b/gopls/integration/govim/cloudbuild.yaml
index c9d610a..aecfd53 100644
--- a/gopls/integration/govim/cloudbuild.yaml
+++ b/gopls/integration/govim/cloudbuild.yaml
@@ -22,15 +22,21 @@
   # uploading artifacts.
   - name: 'gcr.io/$PROJECT_ID/govim-harness:3'
     dir: '/src/govim'
+    volumes:
+      - name: artifacts
+        path: /artifacts
     env:
-      - GOVIM_TESTSCRIPT_WORKDIR_ROOT=/workspace/artifacts
+      - GOVIM_TESTSCRIPT_WORKDIR_ROOT=/artifacts
       - VIM_FLAVOR=vim
     args: ['/workspace/gopls/integration/govim/run_tests_for_cloudbuild.sh']
 
   # The govim tests produce a large number of artifacts; tarball/gzip to reduce
   # roundtrips and save space.
   - name: 'ubuntu'
-    args: ['tar', '-czf', 'artifacts.tar.gz', 'artifacts']
+    volumes:
+      - name: artifacts
+        path: /artifacts
+    args: ['tar', '-czf', 'artifacts.tar.gz', '/artifacts']
 
   # Upload artifacts to GCS.
   - name: 'gcr.io/cloud-builders/gsutil'