executor: reset hasMatch flag for each outer row in merge join

[eurekaka]

What problem does this PR solve?

Fix #9044

What is changed and how it works?

Reset hasMatch flag for each outer row in merge join executor.

Check List

Tests

• Unit test

Code changes

N/A

Side effects

N/A

Related changes

• Need to cherry-pick to the release branch

[eurekaka]

/run-all-tests

[codecov-io]

Codecov Report

Merging #9046 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #9046      +/-   ##
==========================================
+ Coverage   67.25%   67.26%   +<.01%     
==========================================
  Files         371      371              
  Lines       76194    76195       +1     
==========================================
+ Hits        51248    51255       +7     
+ Misses      20412    20409       -3     
+ Partials     4534     4531       -3

Impacted Files	Coverage Δ
executor/merge_join.go	81.6% <100%> (+0.1%)	⬆️
util/systimemon/systime_mon.go	80% <0%> (-20%)	⬇️
expression/schema.go	94.11% <0%> (-0.85%)	⬇️
store/tikv/lock_resolver.go	42.65% <0%> (+0.94%)	⬆️
ddl/delete_range.go	78.85% <0%> (+4.57%)	⬆️

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[XuHuaiyu]

LGTM

[eurekaka]

/run-all-tests

[eurekaka]

/run-unit-test

[zz-jason]

LGTM

[zz-jason]

@eurekaka Please cherry pick it to release-2.1 and release-2.0 branch.