Don't load templates and similar when doing hugo mod graph and similar

[bep]

Which then would fail if there is a template error in the upstream library:

➜  hugo-alpine-test git:(master) ✗ hugo mod graph
hugo: downloading modules …
hugo: collected modules in 3273 ms
Error: add site dependencies: load resources: loading templates: "/Users/bep/dev/hugo_cache/modules/filecache/modules/pkg/mod/github.com/gohugoio/hugo-mod-jslibs/alpinejs/v3@v3.0.0-20210831141009-5f47ae9873c3/layouts/partials/jslibs/alpinejs/v3/script-src.html:4:1": parse failed: template: partials/jslibs/alpinejs/v3/script-src.html:4: undefined variable "$isProd"