Small Improvements to GitHub actions

[morgo]

• Change the endtoend sharded design to a matrix build (easier to maintain)
• Add eatmydata to disable fsyncs, speed up tests slightly. Fixes Run test suite with libeatmydata #5007

My very unscientific test to see if eatmydata made a difference, was to compare the execution time of the main "step" of the test before and after. There is a bit of skew in test execution time, but I think it did make an improvement:

== cluster-endtoend ==
shard 11 9:35  -> 8:59
shard 12 12:05 -> 11:35
shard 13 ??    -> 12:48
shard14 10:08  -> 9:44

== unit ==
 percona56 4:28 -> 4:33
   mysql57 5:25 -> 4:46
   mysql80 5:28 -> 4:55
mariadb101 5:02 -> 4:35
mariadb102 4:55 -> 4:04
mariadb103 4:35 -> 4:37