Add test for `SigningTimeNotValidError` #95

	name: CI
	on: [push, pull_request]

	jobs:
	test:
	name: Test
	strategy:
	matrix:
	go: ['1.12', '1.13', '1.14', '1.15', '1.16']
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v4
	with:
	fetch-depth: 0
	- uses: actions/setup-go@v4
	with:
	go-version: ${{ matrix.go }}
	stable: false
	- name: Test
	run: go vet . && go build . && go test -count=1 -covermode=count -coverprofile=coverage.out .

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