run spectest only when there are tests

Author: Dror Tirosh

.github/workflows/test.yaml

@@ -21,5 +21,5 @@ jobs:
         id: go
       - name: Install staticcheck
         run: go install github.com/lightclient/rpctestgen/cmd/speccheck@latest
-      - name: Install staticcheck
-        run: speccheck -v
+      - name: Run staticcheck
+        run: test -d tests && speccheck -v