Don't run non-node JS tests in parallel in the CI builds

This seems to be broken and sporadically results in "Text file busy"
errors when the tests are run actually in parallel, as is the case in
GitHub CI environment.

.github/workflows/ci.yml

@@ -271,6 +271,12 @@ jobs:
                   [ -s "$NVM_DIR/nvm.sh" ] && . "$NVM_DIR/nvm.sh"
                   nvm use ${VER}
                   ;;
+                *)
+                  # Running tests using v8 or jsc involves creating a custom
+                  # interpreter in Tools/javascript, which is currently broken
+                  # for parallel builds (we attempt to update this interpreter
+                  # while running, resulting in "Text file busy" error).
+                  unset SWIGJOBS
               esac
               ;;