test(datasource/go): Remove go-source header from gitlab fixtures (#32286)

...o/__fixtures__/go-get-gitlab-ee-private-subgroup-api.html

...ce/go/__fixtures__/go-get-gitlab-ee-private-subgroup.html

...datasource/go/__fixtures__/go-get-gitlab-ee-subgroup.html

lib/modules/datasource/go/__fixtures__/go-get-gitlab-ee.html

lib/modules/datasource/go/__fixtures__/go-get-gitlab.html

...s/datasource/go/__fixtures__/go-get-submodule-gitlab.html