title: Error: Compiling RuleSet failed: Properties options are unknown
body: <p>Having upgraded from webpack 4.46.0 to 5.45.1 I am encountering the following error during the build:</p>
  <p><code>Error: Compiling RuleSet failed: Properties options are unknown (at ruleSet[1].rules[6]: [object Object])</code></p>
  <p>Can someone clarify what exactly this error means? I can't work it out as it is so unsemantic. Do I need to set options? If so which?</p>
  <p>It seems to point towards the settings in <code>module.rules</code>, but the 6th entry is just an array of loaders and has no options.</p>
  <p>Previously these were loaded using the <code>loaders</code> property.</p>
  <pre><code>      module: {
          rules: [
            ...5 other entries...,
            {
              test: /\/custom-file.js$/,
              use: [
                'cache-loader',
                path.resolve(__dirname, '../build/package/custom-webpack-loader.js'),
              ],
            },
          ],
        },
  </code></pre>