Drop "latest" from e2e workflow

k6 v0.45.1 is failing with go get and go getting with "latest" causes
our CI to fail, too. It was working so far, but with the regression
in v0.45.0, the CI task has stopped working.

.github/workflows/e2e.yml

@@ -44,7 +44,7 @@ jobs:
           which go
           go version
 
-          GOPRIVATE="go.k6.io/k6" xk6 build latest \
+          GOPRIVATE="go.k6.io/k6" xk6 build \
             --output ./k6extension \
             --with github.com/grafana/xk6-browser=.
           ./k6extension version