use .RelPermalink instead of .URL for active check

[imomaliev]

Page does not have URL attribute

currently hugo server -b localhost gives

$ hugo server -b localhost
Watching for changes in site/{archetypes,assets,content,layouts,static}
Watching for config changes in site/config.toml
Start building sites …
hugo v0.134.3+extended darwin/arm64 BuildDate=2024-09-19T14:28:20Z VendorInfo=brew

ERROR render of "page" failed: "site/layouts/_default/baseof.html:109:5": execute of template failed: template: _default/single.html:109:5: executing "_default/single.html" at <partial "site-header.html" .>: error calling partial: "site/layouts/partials/site-header.html:28:26": execute of template failed: template: partials/site-header.html:28:26: executing "partials/site-header.html" at <$.URL>: can't evaluate field URL in type *hugolib.pageState
ERROR render of "section" failed: "site/layouts/_default/baseof.html:109:5": execute of template failed: template: _default/list.html:109:5: executing "_default/list.html" at <partial "site-header.html" .>: error calling partial: "site/layouts/partials/site-header.html:28:26": execute of template failed: template: partials/site-header.html:28:26: executing "partials/site-header.html" at <$.URL>: can't evaluate field URL in type *hugolib.pageState
Built in 64 ms
Error: error building site: render: failed to render pages: render of "page" failed: "site/layouts/_default/baseof.html:109:5": execute of template failed: template: _default/single.html:109:5: executing "_default/single.html" at <partial "site-header.html" .>: error calling partial: "site/layouts/partials/site-header.html:28:26": execute of template failed: template: partials/site-header.html:28:26: executing "partials/site-header.html" at <$.URL>: can't evaluate field URL in type *hugolib.pageState

This PR fixes that