chore(deps): update sigstore/cosign-installer action to v4 (#90)

Signed-off-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/build.yml

@@ -62,7 +62,7 @@ jobs:
 
       # Even if we're testing we sign the images, so we can push them to production later if that's required
       - name: Install cosign
-        uses: sigstore/cosign-installer@398d4b0eeef1380460a10c8013a76f728fb906ac # v3
+        uses: sigstore/cosign-installer@cad07c2e89fa2edd6e2d7bab4c1aa38e53f76003 # v4.1.1
         # See https://github.blog/security/supply-chain-security/safeguard-container-signing-capability-actions/
         # and https://github.com/actions/starter-workflows/blob/main/ci/docker-publish.yml for more details on
         # how to use cosign.