ci: enable test shuffle and fix tests

[alexandear]

This PR extends go test with -shuffle flag:

-shuffle off,on,N
    Randomize the execution order of tests and benchmarks.
    It is off by default. If -shuffle is set to on, then it will seed
    the randomizer using the system clock. If -shuffle is set to an
    integer N, then N will be used as the seed value. In both cases,
    the seed will be reported for reproducibility.

Also, fix conflicting tests.

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[sagikazarmark]

Sounds like a good idea, but looks like the tests are failing. :/

[alexandear]

@sagikazarmark the tests are failing because they depend on each other. I'll try to fix it in this PR.

[alexandear]

@sagikazarmark fixed tests