Add webpack EnvironmentPlugin (go-gitea#32661)

Fixes: go-gitea#32660

Environment vars in Webpack need to be declared in the config, otherwise
they will not be elimininated during compilation.

webpack.config.js

@@ -17,7 +17,7 @@ import tailwindcssNesting from 'tailwindcss/nesting/index.js';
 import postcssNesting from 'postcss-nesting';
 
 const {EsbuildPlugin} = EsBuildLoader;
-const {SourceMapDevToolPlugin, DefinePlugin} = webpack;
+const {SourceMapDevToolPlugin, DefinePlugin, EnvironmentPlugin} = webpack;
 const formatLicenseText = (licenseText) => wrapAnsi(licenseText || '', 80).trim();
 
 const glob = (pattern) => fastGlob.sync(pattern, {
@@ -213,6 +213,10 @@ export default {
       __VUE_PROD_DEVTOOLS__: false, // do not enable devtools support in production
       __VUE_PROD_HYDRATION_MISMATCH_DETAILS__: false, // https://github.com/vuejs/vue-cli/pull/7443
     }),
+    // all environment variables used in bundled js via process.env must be declared here
+    new EnvironmentPlugin({
+      TEST: 'false',
+    }),
     new VueLoaderPlugin(),
     new MiniCssExtractPlugin({
       filename: 'css/[name].css',