Fix bootstrapApplication to use the main-component (angular#32391)

There seems to be an trailing comma here that doesn't exist in the template and causes this replacement to be a no-op.

(cherry picked from commit 27309fd)

Author: tjlav5

docs/src/app/shared/stackblitz/stackblitz-writer.ts

@@ -215,8 +215,8 @@ export class StackBlitzWriter {
       // Replace `bootstrapApplication(MaterialDocsExample,`
       // will be replaced as `bootstrapApplication(ButtonDemo,`
       fileContent = fileContent.replace(
-        /bootstrapApplication\(MaterialDocsExample,/g,
-        `bootstrapApplication(${mainComponentName},`,
+        /bootstrapApplication\(MaterialDocsExample/g,
+        `bootstrapApplication(${mainComponentName}`,
       );
 
       const dotIndex = data.indexFilename.lastIndexOf('.');