feat: support config junit reporter className with env

docs/config/index.md

@@ -483,7 +483,7 @@ Custom reporters for output. Reporters can be [a Reporter instance](https://gith
   - `'basic'` - give a reporter like default reporter in ci
   - `'verbose'` - keep the full task tree visible
   - `'dot'` -  show each task as a single dot
-  - `'junit'` - JUnit XML reporter (you can configure `testsuites` tag name with `VITEST_JUNIT_SUITE_NAME` environmental variable)
+  - `'junit'` - JUnit XML reporter (you can configure `testsuites` tag name with `VITEST_JUNIT_SUITE_NAME` environmental variable, and `classname` tag property with `VITEST_JUNIT_CLASSNAME`)
   - `'json'` -  give a simple JSON summary
   - `'html'` -  outputs HTML report based on [`@vitest/ui`](/guide/ui)
   - `'hanging-process'` - displays a list of hanging processes, if Vitest cannot exit process safely. This might be a heavy operation, enable it only if Vitest consistently cannot exit process

packages/vitest/src/node/reporters/junit.ts

@@ -168,7 +168,7 @@ export class JUnitReporter implements Reporter {
   async writeTasks(tasks: Task[], filename: string): Promise<void> {
     for (const task of tasks) {
       await this.writeElement('testcase', {
-        classname: filename,
+        classname: process.env.VITEST_JUNIT_CLASSNAME ?? filename,
         name: task.name,
         time: getDuration(task),
       }, async () => {