Even if test automation has larger potential benefits for DevOps than manual testing, manual testing will always be an important part of software development. If nothing else, we will need to perform our tests manually at least once in order to automate them.
Acceptance testing in particular is hard to replace, even though there have been attempts to do so. Software requirement specifications can be terse and hard to understand even for the people developing the features that implement those requirements. In these cases, quality assurance people with their eyes on the ball are invaluable and irreplaceable.
The things that make manual testing easier are the same things that make automated integration testing easier as well, so there is a synergy to achieve between the different testing strategies.
In order to have happy quality assurance personnel, you need to:
Manage test data, primarily the contents of backend databases, so that tests give the same results when you run them repeatedly...