fix(expect)!: fix toThrow("") behavior by reverting #6710 (#9643)

Author: hi-ogawa

packages/expect/src/jest-expect.ts

@@ -748,8 +748,7 @@ export const JestChaiExpect: ChaiPlugin = (chai, utils) => {
         || typeof expected === 'undefined'
         || expected instanceof RegExp
       ) {
-        // Fixes the issue related to `chai` <https://github.com/vitest-dev/vitest/issues/6618>
-        return this.throws(expected === '' ? /^$/ : expected)
+        return this.throws(expected)
       }
 
       const obj = this._obj

test/core/test/jest-expect.test.ts

@@ -115,7 +115,10 @@ describe('jest-expect', () => {
     }).toThrow('')
     expect(() => {
       throw new Error('error')
-    }).not.toThrow('')
+    }).toThrow('') // empty string is a substring of any error message
+    expect(() => {
+      throw new Error('error')
+    }).not.toThrow(/^$/) // use regex to explicitly test non-empty error message
     expect([1, 2, 3]).toHaveLength(3)
     expect('abc').toHaveLength(3)
     expect('').not.toHaveLength(5)