Update mixin-deep to 1.3.2

What does this MR do?

Updates mixin-deep from 1.3.1 to 1.3.2 to address a Prototype Pollution vulnerability, which exists in mixin-deep package, versions >=2.0.0 <2.0.1 || <1.3.2 (CVE-2019-10746).

• from: https://www.npmjs.com/package/mixin-deep/v/1.3.1
• to: https://www.npmjs.com/package/mixin-deep/v/1.3.2
• 2 commits (github.com): https://github.com/jonschlinkert/mixin-deep/compare/1.3.1...1.3.2
• Synk ID: https://app.snyk.io/vuln/SNYK-JS-MIXINDEEP-450212

mixin-deep package is required by webpack.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [n/a] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• [n/a] Style guides
• [n/a] Database guides
• [n/a] Separation of EE specific content

Performance and testing

• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers

Security

• [n/a] Label as security and @ mention @gitlab-com/gl-security/appsec
• [n/a] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [n/a] Security reports checked/validated by a reviewer from the AppSec team

Closes #63945 (closed)