Fix dark mode secondary text colour broken by postcss-color-mod-function v4 (#1040)

* 🐛 Fix dark mode secondary text colour broken by postcss-color-mod-function v4

The color-mod(var(--color-secondary-text) l(-22%)) value compiled to
#000 after postcss-color-mod-function was bumped from v3 to v4, making
tags, post meta, byline and pagination text invisible on dark backgrounds.

Replace with var(--color-secondary-text) directly. #979797 gives ~4.6:1
contrast on the dark mode background and sits correctly below the #fff
primary text in the visual hierarchy. Same fix applied to the auto-color
media query variant.

* Fix gulp zip task broken by gulp-zip v6 API change

gulp-zip v6 switched to a named export. Update require() to use .default
to restore the zip build task.

* Revert "Fix gulp zip task broken by gulp-zip v6 API change"

This reverts commit 9a71b49.

Author: jonhickman

assets/built/screen.css

@@ -2193,7 +2193,7 @@ html.dark-mode .post-card-image {
 }
 
 html.dark-mode :is(.post-card-tags, .post-card-meta, .article-tag a, .byline-meta-content, .pagination .page-number) {
-    color: color-mod(var(--color-secondary-text) l(-22%));
+    color: var(--color-secondary-text);
 }
 
 html.dark-mode .post-card-featured {
@@ -2387,7 +2387,7 @@ html.dark-mode .footer-cta-title {
     }
 
     html.auto-color :is(.post-card-tags, .post-card-meta, .article-tag a, .byline-meta-content, .pagination .page-number) {
-        color: color-mod(var(--color-secondary-text) l(-22%));
+        color: var(--color-secondary-text);
     }
 
     html.auto-color .post-card-featured {