chore: modify the typecheck as prompted

[Fish-pro]

Signed-off-by: Fish-pro zechun.chen@daocloud.io

What this PR does / why we need it:

➜  gatekeeper git:(master) golangci-lint run -c .golangci.yaml
apis/status/v1beta1/constraintpodstatus_types_test.go:4:2: "strings" imported but not used (typecheck)
        "strings"
        ^
pkg/readiness/ready_tracker_test.go:574:21: invalid operation: cannot compare tc.tracker != nil (operator != not defined on untyped nil) (typecheck)
                        if tc.tracker != nil {
                                         ^

Which issue(s) this PR fixes (optional, using fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when the PR gets merged):
Fixes #

Special notes for your reviewer:

[acpana]

should this be reverted?

[Fish-pro]

I've already found it, and I understand it's golang-lint problem, but in order to pass the check, I've made an irrelevant change

[maxsmythe]

LGTM

[codecov-commenter]

Codecov Report

Base: 53.54% // Head: 53.59% // Increases project coverage by +0.04% 🎉

Coverage data is based on head (81cd9f7) compared to base (05638fd).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2553      +/-   ##
==========================================
+ Coverage   53.54%   53.59%   +0.04%     
==========================================
  Files         120      120              
  Lines       10634    10634              
==========================================
+ Hits         5694     5699       +5     
+ Misses       4506     4502       -4     
+ Partials      434      433       -1     

Flag	Coverage Δ
unittests	53.59% <ø> (+0.04%)	⬆️

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

Impacted Files	Coverage Δ
...onstrainttemplate/constrainttemplate_controller.go	59.33% <0.00%> (+1.19%)	⬆️

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[Fish-pro]

@sozercan Thanks for update branch，Do you need me to rebase?

[sozercan]

@Fish-pro thank you! no need, since we got the tests unblocked with #2573, i am merging to master for those that are already approved so i can merge them.