cli: fix `--output-signature` and `--output-certificate` (sigstore#133)

* cli: fix `--output-signature` and `--output-certificate`

Signed-off-by: William Woodruff <william@trailofbits.com>

* sigstore: 0.6.1

Signed-off-by: William Woodruff <william@trailofbits.com>

sigstore: 0.6.0 (sigstore#132)

Signed-off-by: William Woodruff <william@trailofbits.com>

sigstore: 0.5.1 (sigstore#118)

Signed-off-by: William Woodruff <william@trailofbits.com>

sigstore: 0.5.1rc2

Signed-off-by: William Woodruff <william@trailofbits.com>

workflows/release: put sigs and certs in their own directory

To avoid confusing twine.

Signed-off-by: William Woodruff <william@trailofbits.com>

sigstore: 0.5.0 (sigstore#111)

Signed-off-by: William Woodruff <william@trailofbits.com>

Version 0.4.2 (sigstore#93)

version: 0.4.1 (sigstore#82)

Signed-off-by: William Woodruff <william@trailofbits.com>

version: 0.4.0 (sigstore#78)

Signed-off-by: William Woodruff <william@trailofbits.com>

version: 0.3.1