Backport of GOPATH is being set incorrectly in latest CircleCI machin…

…e image into release/1.8.x (#15291)

* backport of commit b6ea75f

* backport of commit 0bf0f09

Co-authored-by: Christopher Swenson <christopher.swenson@hashicorp.com>

.circleci/config/commands/@caches.yml

@@ -18,9 +18,9 @@ restore_go_mod_cache_permissive:
     - restore_cache:
         name: Restore closest matching go modules cache
         keys:
-          - &gocachekey v1.4-{{checksum "go.sum"}}-{{checksum "sdk/go.sum"}}-{{checksum "api/go.sum"}}
-          -             v1.4-{{checksum "go.sum"}}-{{checksum "sdk/go.sum"}}
-          -             v1.4-{{checksum "go.sum"}}
+          - &gocachekey v1.5-{{checksum "go.sum"}}-{{checksum "sdk/go.sum"}}-{{checksum "api/go.sum"}}
+          -             v1.5-{{checksum "go.sum"}}-{{checksum "sdk/go.sum"}}
+          -             v1.5-{{checksum "go.sum"}}
 restore_go_mod_cache:
   steps:
     - restore_cache:
@@ -40,6 +40,8 @@ refresh_go_mod_cache:
     - run:
         name: go mod download
         command: |
+          # set GOPATH explicitly to download to the right cache
+          export GOPATH=$HOME/go
           # go list ./... forces downloading some additional versions of modules that 'go mod
           # download' misses. We need this because we make use of go list itself during
           # code generation in later builds that rely on this module cache.