unstable test TestModifyOneByte/encrypted

[tisonkun]

This line now creates unstable test

[2021-09-23T16:00:22.934Z] --- FAIL: TestModifyOneByte (0.00s)
[2021-09-23T16:00:22.934Z]     --- FAIL: TestModifyOneByte/encrypted (0.00s)
[2021-09-23T16:00:22.934Z]         checksum_test.go:179: 
[2021-09-23T16:00:22.934Z]             	Error Trace:	checksum_test.go:179
[2021-09-23T16:00:22.934Z]             	            				checksum_test.go:150
[2021-09-23T16:00:22.934Z]             	Error:      	Target error should be in err chain:
[2021-09-23T16:00:22.934Z]             	            	expected: "error checksum"
[2021-09-23T16:00:22.934Z]             	            	in chain: 
[2021-09-23T16:00:22.934Z]             	Test:       	TestModifyOneByte/encrypted

Originally posted by @tisonkun in #26252 (comment)

[tisonkun]

@Ranxy please take a look. Also we almost use require package for assertion.

[tisonkun]

--- FAIL: TestModifyOneByte (0.00s)
    --- FAIL: TestModifyOneByte/encrypted (0.00s)
        checksum_test.go:179: 
            	Error Trace:	checksum_test.go:179
            	            				checksum_test.go:150
            	Error:      	Target error should be in err chain:
            	            	expected: "error checksum"
            	            	in chain: 
            	Test:       	TestModifyOneByte/encrypted
            	Messages:   	err: <nil>
FAIL
exit status 1
FAIL	github.com/pingcap/tidb/util/checksum	0.252s

you can use a script to forever run util failure

while go test -count=1; do; done

[tisonkun]

... also cc @mmyj @wshwsh12 since @mmyj is the author of this package and @wshwsh12 add the original test. This test is originally TestTiCase3646.

[Ranxy]

/assign

[github-actions]

Please check whether the issue should be labeled with 'affects-x.y' or 'fixes-x.y.z', and then remove 'needs-more-info' label.

[tisonkun]

@Ranxy thank you for fixing this!