[upd] migrate .eslintrc.json to eslint.config.mjs

The migration was done by the following steps, firts prepare the node enviroment
an open a bash in this environment::

    $ make clean nvm.nodejs
    ...
    $ ./manage nvm.bash
    $ which npx
    searxng/.nvm/versions/node/v23.5.0/bin/npx

In this environment the migration command from [1] is started::

    $ npx @eslint/migrate-config .eslintrc.json
    Need to install the following packages:
    @eslint/migrate-config@1.3.5
    Migrating .eslintrc.json

    Wrote new config to ./eslint.config.mjs

    You will need to install the following packages to use the new config:
    - globals
    - @eslint/js
    - @eslint/eslintrc

    You can install them using the following command:

    npm install globals @eslint/js @eslint/eslintrc -D

    The following messages were generated during migration:
    - The 'node' environment is used, so switching sourceType to 'commonjs'.

[1] https://eslint.org/docs/latest/use/configure/migration-guide#migrate-your-config-file

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/static/themes/simple/gruntfile.js

@@ -35,7 +35,7 @@ module.exports = function (grunt) {
     },
     eslint: {
       options: {
-        overrideConfigFile: '.eslintrc.json',
+        overrideConfigFile: 'eslint.config.mjs',
         failOnError: true,
         fix: grunt.option('fix')
       },