ci: Report test coverage (#144)

diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index ea89d89..44e56bc 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -51,4 +51,4 @@
       - name: Go mod verify
         run: go mod verify
       - name: Run tests
-        run: go test -v ./...
+        run: go test -cover -v ./...