Fix the value for `APISecretNamespaceKey`
Fix the value for `APISecretNamespaceKey`

Related to https://github.com/tektoncd/pipeline/pull/5450.

The key for APISecretNamespace in the configmap is named `api-token-secret-namespace`,
but the value of `APISecretNamespaceKey` in `pkg/resolution/resolver/git/config.go`
is `api-token-namespace`. This will cause resolver to fail to get API token.

In this PR, we use the correct key name `api-token-secret-namespace`.

Signed-off-by: Chuang Wang <5161cce741fb1626e53fe819fa9eba1da871a86c@google.com>

tektoncd/pipeline,tektoncd/pipeline