ci: doc-build: use --no-verbose when using wget

The -q flag supresses all wget output, even when there is a failure.
This makes it difficult to diagnose CI failures when the download fails.
The --no-verbose flag is a better choice: it is silent enough but it
always shows the outcome.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>