For one of the Phpstan upgrades, some message text had changed so drastically that the only practical solution at the time was to move the messages from phpstan-baseline.neon to phpstan.neon.dist. This was not ideal, but it allowed us time to move on and study the errors, which I have now done. At one point, Parser is expecting a variable to be an array, and that was not clear from the code. If not an array, the code will error out (which was Phpstan's concern); I have changed it to throw an exception instead. This satisfies Phpstan, and I can get the message out of neon.dist (without needing to restore it to baseline). Unsurprisingly, the exception was never thrown in the existing test suite, although I added a couple of tests to exercise that code.
In Helper/Dimension, Phpstan flagged a statement inappropriately. I suppressed the message using an annotation and filed a bug report https://github.com/phpstan/phpstan/issues/7563. A fix for the problem was merged yesterday, which is good, but it puts us in a tenuous position. The annotation is needed now, but, when the fix is inevitably pushed to the version we use, the no-longer-needed annotation will trigger a different message. Recode so that neither the current nor the future versions will issue a message, eliminating the annotation in the process.