Flaky test: secrets "bar" not found in namespace controller test

[zoetrope]

Describe the bug

Secret "bar" sometimes not found in the namespace controller test.

https://github.com/cybozu-go/accurate/runs/3891153514?check_suite_focus=true

• Failure [0.614 seconds]
Namespace controller
/home/runner/work/accurate/accurate/controllers/namespace_controller_test.go:39
  should implement template namespace correctly [It]
  /home/runner/work/accurate/accurate/controllers/namespace_controller_test.go:84

  Unexpected error:
      <*errors.StatusError | 0xc000a69ea0>: {
          ErrStatus: {
              TypeMeta: {Kind: "", APIVersion: ""},
              ListMeta: {
                  SelfLink: "",
                  ResourceVersion: "",
                  Continue: "",
                  RemainingItemCount: nil,
              },
              Status: "Failure",
              Message: "secrets \"bar\" not found",
              Reason: "NotFound",
              Details: {Name: "bar", Group: "", Kind: "secrets", UID: "", Causes: nil, RetryAfterSeconds: 0},
              Code: 404,
          },
      }
      secrets "bar" not found
  occurred

  /home/runner/work/accurate/accurate/controllers/namespace_controller_test.go:199
------------------------------
SSSTEP: tearing down the test environment


Summarizing 1 Failure:

[Fail] Namespace controller [It] should implement template namespace correctly 
/home/runner/work/accurate/accurate/controllers/namespace_controller_test.go:199

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[ymmt2005]

This might have been caused by the bug fixed in #29.