Update testing.md (#28190)

Removed "`" with "'".



## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [x] Make sure the linting passes

docs/testing.md

@@ -175,7 +175,7 @@ module.exports = {
 
     // Handle image imports
     // https://jestjs.io/docs/webpack#handling-static-assets
-    '^.+\\.(jpg|jpeg|png|gif|webp|svg)$': `<rootDir>/__mocks__/fileMock.js`,
+    '^.+\\.(jpg|jpeg|png|gif|webp|svg)$': '<rootDir>/__mocks__/fileMock.js',
   },
   testPathIgnorePatterns: ['<rootDir>/node_modules/', '<rootDir>/.next/'],
   transform: {