This is a reasonable choice to make depending on the complexity of your project. For the projects I've been on, the latest version plus the test suite is enoug

This is a reasonable choice to make depending on the complexity of your project. For the projects I've been on, the latest version plus the test suite is enough to catch weirdness creeping in and, as a side benefit, it gets fixed faster than if it were pinned. Sometimes the issue really is caused by the base image and it is easier to get a fix merged if the issue was caused quite recently because the developers responsible see early reports of issues as more endemic than if they're reported days or weeks later.