[ArrayManager] TST: run all tests with separate not slow / slow build
xref #39146 

@jreback @jbrockmendel as discussed, this splits the current actions build with ArrayManager in two and runs the full test suite with slow / not slow markers. nice.  any estimate how this affects CI runtime? >  any estimate how this affects CI runtime?

Note that with this PR, not much changes (we were already running almost all tests in this build). It is https://github.com/pandas-dev/pandas/pull/40496 that is adding tests to all other builds And to answer your actual question: this added one build (for the slow tests) that takes 25m. thanks @jorisvandenbossche very nice