[DO NOT MERGE]bump up go version to v1.15.3

[wy65701436]

Signed-off-by: wang yan wangyan@vmware.com

[codecov]

Codecov Report

Merging #13326 into release-2.1.0 will increase coverage by 0.00%.
The diff coverage is n/a.

@@              Coverage Diff               @@
##           release-2.1.0   #13326   +/-   ##
==============================================
  Coverage          61.86%   61.86%           
==============================================
  Files                913      913           
  Lines              54613    54613           
  Branches            2014     2014           
==============================================
+ Hits               33784    33787    +3     
+ Misses             17069    17066    -3     
  Partials            3760     3760           

Flag	Coverage Δ
#unittests	61.86% <ø> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
.../src/pkg/permission/evaluator/rbac/casbin_match.go	90.00% <0.00%> (-10.00%)	⬇️
....com/goharbor/harbor/src/controller/event/topic.go	10.81% <0.00%> (+1.80%)	⬆️
...ortal/src/lib/components/config/gc/gc.component.ts	57.74% <0.00%> (+2.81%)	⬆️
...bor/harbor/src/replication/registry/healthcheck.go	47.61% <0.00%> (+4.76%)	⬆️
.../src/controller/event/handler/auditlog/auditlog.go	63.15% <0.00%> (+5.26%)	⬆️

[wy65701436]

per issue golang/go#39568, it may break the user's scenario, just hold the golang upgrade.

[wy65701436]

cc @dirkmueller

[wy65701436]

close it as the golang version has been upgraded to v1.15.6