In the documentation it says
X.Y
versions are aliases for recentX.Y.Z
releases pre-installed on the build images.
I have in my .travis.yml
dist: bionic
language: php
php:
- '7.4'
Today this results in PHP 7.4.2 being used. (See my job)
I can see that 7.4.29 is in your system so how about updating the 7.4 image. A PHP bug in that old version is causing my tests to fail.