Update column type for MySQL sessions table

[beejaz]

This page hasnt been updated with this fix #12641 for "Preparing the Database to Store Sessions" on MySQL db, causing error:

SQLSTATE[22003]: Numeric value out of range: 1264 Out of range value for column 'sess_lifetime' at row 1

Its fixed by changing MEDIUMINT to INTEGER UNSIGNED for sess_lifetime column.

Its the same miss in 4.4, 5.0 and 5.1

[javiereguiluz]

Closing in favor of #13765.

@beejaz thanks for this contribution. However, it's not necessary because you did the same change in another pull request that targets 4.4, a lower branch. Because of how Symfony Docs maintainers merge contributions, you only need to submit a pull request to fix the issue in the lowest maintained branch that contains the error (4.4 in this case). Later, when merging things, mergers take care of merging the same change in all supported branches up to master. That's why we're closing this and keeping only the pull request targeted at 4.4 branch. Thanks!

[beejaz]

Thanks and sorry for missunderstanding!