Support CHECK constraints for MySQL8

[k1LoW]

Fix #450

[github-actions]

Code Metrics Report

	main (62ece04)	#452 (655dc20)	+/-
Coverage	67.7%	65.5%	-2.2%
Code to Test Ratio	1:0.4	1:0.4	-0.0
Test Execution Time	2m37s	4m16s	+1m39s

Details

  |                     | main (62ece04) | #452 (655dc20) |  +/-   |
  |---------------------|----------------|----------------|--------|
- | Coverage            |          67.7% |          65.5% |  -2.2% |
  |   Files             |             35 |             35 |      0 |
  |   Lines             |           3423 |           3445 |    +22 |
- |   Covered           |           2317 |           2255 |    -62 |
- | Code to Test Ratio  |          1:0.4 |          1:0.4 |   -0.0 |
  |   Code              |           8915 |           8963 |    +48 |
  |   Test              |           3882 |           3882 |      0 |
- | Test Execution Time |          2m37s |          4m16s | +1m39s |

Code coverage of files in pull request scope (74.1% → 72.8%)

Files	Coverage	+/-
drivers/mysql/mysql.go	72.8%	-1.3%

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Reported by octocov