**What does this PR do?**

This PR bumps the required ruby version for the gem to Ruby 2.5.0.

**Motivation:**

We're not actively targetting any older release than that (or testing
with), so might as well clarify that in our gemspec.

**Additional Notes:**

N/A

**How to test the change?**

Validate CI is still green :)

Validate that the required Ruby version shows up on rubygems.org
once we publish the update.

[NO-TICKET] Bump required Ruby version to 2.5

These are no longer needed now that Ruby 3.4.0 stable is out.

These were the output of running
`bundle exec rake add_source VERSION=3.4.0`

For some weird reason the `archive-tar-minitar` gem was getting stuck
calling fsync so I had to `bundle open` the gem and disable the fsync
code.

Also manually removed the `*.inc` files.

These are no longer needed now that Ruby 3.4.0 stable is out.

The missing patchlevel is due to an upstream bug (which is the reason
why Ruby 3.4.1 was immediately released after 3.4.0), so let's
manually account for it.

…e-headers

[PROF-11203] Add Ruby 3.4.0 stable headers and bump gem version to 3.4.0