Bump Puma to 5.3.2

What does this MR do?

This updates Puma from version 5.1.1 to 5.3.2 (the latest release at the time I write this.)

There are several interesting changes that happened over the past two point releases, including multiple bugs and security vulnerabilities fixed as well as potential performance improvements.

For a full change log, have a look here: https://github.com/puma/puma/blob/master/History.md#532--2021-05-21

We can also drop the tempfile fix that Sean added, since these changes have been upstreamed.

Smoke testing

The changes are deployed to https://gitlab-review-mk-puma-5-vooqas.gitlab-review.app

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.