Add missing T.Helper() in testutil.Check* as required

[briandealwis]

Turns

--- FAIL: TestWalk (0.02s)
    --- FAIL: TestWalk/should_return_correct_k8_configs_and_build_files (0.00s)
        util.go:69: int differ (-got, +want):   int(
            - 	4,
            + 	5,
              )
        util.go:69: string differ (-got, +want):   strings.Join({
              	"/var/folders/mx/_6wvyq4n3psb4nj95d8ycpv80000gn/T/skaffold7141983",
              	"63/",
            - 	"maven/pom.xml",
            + 	"gradle-kotlin/build.gradle.kts",
              }, "")

into

--- FAIL: TestWalk (0.02s)
    --- FAIL: TestWalk/should_return_correct_k8_configs_and_build_files (0.00s)
        init_test.go:281: int differ (-got, +want):   int(
            - 	4,
            + 	5,
              )
        init_test.go:283: string differ (-got, +want):   strings.Join({
              	"/var/folders/mx/_6wvyq4n3psb4nj95d8ycpv80000gn/T/skaffold9003403",
              	"91/",
            - 	"maven/pom.xml",
            + 	"gradle-kotlin/build.gradle.kts",
              }, "")

[codecov]

Codecov Report

Merging #2913 into master will not change coverage.
The diff coverage is n/a.