Merge 5.5 into 5.x

[mongodb-php-bot]

Merge new changes from 5.5 into 5.x.

Commits

• Use DB tx manager in `ManagesTransactions` trait (PHPLIB-373 Use DatabaseTransactionsManager in ManagesTransactions trait #3443): dee170a

Resolving conflicts

To resolve any conflicts, check out the temporary branch and run the following command:

git merge 5.x -m "Resolve conflicts in 5.x"

Ignoring changes

To ignore from the remote branch, first reset the temporary branch to 5.x and manually merge using the `ours` merge strategy:

git reset --hard 5.x
git merge --strategy=ours 5.5 -m "Ignore changes from 5.5"

Then, push the temporary branch to upate the pull request.