test: make several slow package unit test support run parallel

[glorv]

What problem does this PR solve?

make several package unit test support run unit test parallel to speed up unit test running

What is changed and how it works?

some unit test need to change global variables to set up running environment, thus make it impossible to run in parallel. By move these test into independent test suite and use SerialSuites instead of Suite, we can make sure they will still run in serial, so it will be safe to open the parallel flag for other tests.

Here is the result:
Before change:

>  go test -v -vet=off -p 10 -race github.com/pingcap/tidb/planner/core
ok  	github.com/pingcap/tidb/planner/core	110.140s

> go test -v -vet=off -p 10 -race github.com/pingcap/tidb/session
ok  	github.com/pingcap/tidb/session	123.002s

After change:

> go test -v -vet=off -p 10 -race github.com/pingcap/tidb/planner/core -check.p=true
ok  	github.com/pingcap/tidb/planner/core	41.524s

> go test -v -vet=off -p 10 -race github.com/pingcap/tidb/session -check.p=true
ok  	github.com/pingcap/tidb/session	95.673s

Check List

Tests

• unit tests

Code changes

Side effects

Related changes

[CLAassistant]

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2 out of 3 committers have signed the CLA.

✅ AilinKid
✅ sre-bot
❌ gaolei

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[AilinKid]

/run-all-tests

[codecov]

Codecov Report

Merging #13431 into master will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             master     #13431   +/-   ##
===========================================
  Coverage   80.1686%   80.1686%           
===========================================
  Files           471        471           
  Lines        114062     114062           
===========================================
  Hits          91442      91442           
  Misses        15465      15465           
  Partials       7155       7155

[tiancaiamao]

/run-all-tests

[eurekaka]

LGTM

[tiancaiamao]

LGTM

[tiancaiamao]

/merge

[sre-bot]

/run-all-tests

[sre-bot]

@glorv merge failed.

[glorv]

/run-all-tests

[glorv]

/run-integration-copr-test