Update mini-css-extract-plugin, remove postcss (#23520)

Follow-up and proper fix for
https://github.com/go-gitea/gitea/pull/23504

Update to
[mini-css-extract-plugin@2.7.4](https://github.com/webpack-contrib/mini-css-extract-plugin/releases/tag/v2.7.4)
which fixes our specific issue described in
https://github.com/webpack-contrib/css-loader/issues/1503 and which
allows us to again drop the postcss dependency.

Backport of this is not necessary as I have included it in
https://github.com/go-gitea/gitea/pull/23508.

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

package.json

@@ -30,12 +30,9 @@
     "katex": "0.16.4",
     "license-checker-webpack-plugin": "0.2.1",
     "mermaid": "10.0.2",
-    "mini-css-extract-plugin": "2.7.2",
+    "mini-css-extract-plugin": "2.7.4",
     "monaco-editor": "0.34.1",
     "monaco-editor-webpack-plugin": "7.0.1",
-    "postcss-import": "15.1.0",
-    "postcss-loader": "7.0.2",
-    "postcss-url": "10.1.3",
     "pretty-ms": "8.0.0",
     "sortablejs": "1.15.0",
     "swagger-ui-dist": "4.15.5",
@@ -46,7 +43,7 @@
     "vue-bar-graph": "2.0.0",
     "vue-loader": "17.0.1",
     "vue3-calendar-heatmap": "2.0.0",
-    "webpack": "5.76.0",
+    "webpack": "5.76.2",
     "webpack-cli": "5.0.1",
     "workbox-routing": "6.5.4",
     "workbox-strategies": "6.5.4",

web_src/css/themes/theme-auto.css

@@ -1,2 +1 @@
-/* This import requires postcss-import so the media query is preserved in the output */
 @import "./theme-arc-green.css" (prefers-color-scheme: dark);

webpack.config.js

@@ -145,23 +145,10 @@ export default {
             loader: 'css-loader',
             options: {
               sourceMap: true,
-              importLoaders: 1,
               url: {filter: filterCssImport},
               import: {filter: filterCssImport},
             },
           },
-          {
-            loader: 'postcss-loader', /* for conditional import in theme-auto.css */
-            options: {
-              sourceMap: true,
-              postcssOptions: {
-                plugins: [
-                  'postcss-import',
-                  'postcss-url',
-                ],
-              },
-            },
-          },
         ],
       },
       {