ci: ensure build-distros uses the same go.mod file as normal builds

When running 'make tools' the go command indirectly edits both the
go.mod and go.sum files in ways that can cause the later build of consul
itself to build with slightly different dependencies than it normally
would.

.circleci/config.yml

@@ -146,7 +146,10 @@ jobs:
     resource_class: large
     steps:
       - checkout
-      - run: make tools
+      - run: |
+          make tools
+          # restore any go.{mod,sum} files that were updated indirectly
+          git reset --hard HEAD
       - run: ./build-support/scripts/build-local.sh
 
       # save dev build to CircleCI