Fix broken import replacement when createAuth isn't the last import

Fixes #11588

packages/storybook/src/plugins/mock-auth.ts

@@ -6,13 +6,12 @@ export function mockAuth(): PluginOption {
     enforce: 'pre',
     transform(code: string, id: string) {
       if (id.includes('web/src/auth')) {
-        // remove any existing import of `createAuth` without affecting
-        // anything else.
-        // this regex defines 3 capture groups, where the second is
-        // `createAuth` — we want to remove that one.
+        // Remove any existing import of `createAuth` without affecting anything else.
+        // This regex defines 4 capture groups, where the second is `createAuth` and 
+        // the third is an (optional) comma for subsequent named imports — we want to remove those two.
         code = code.replace(
-          /(import\s*{\s*[^}]*)(\bcreateAuth\b)([^}]*})/,
-          '$1$3',
+          /(import\s*{\s*[^}]*)(\bcreateAuth\b)(,?)([^}]*})/,
+          '$1$4',
         )
         // Add import to mocked `createAuth` at the top of the file.
         code =