chore(deps): Bump blinklabs-io/mithril-signer

Bumps [blinklabs-io/mithril-signer](https://github.com/blinklabs-io/docker-mithril-signer) from 0.2.268-1 to 0.2.273-1.
- [Release notes](https://github.com/blinklabs-io/docker-mithril-signer/releases)
- [Commits](blinklabs-io/docker-mithril-signer@v0.2.268-1...v0.2.273-1)

---
updated-dependencies:
- dependency-name: blinklabs-io/mithril-signer
  dependency-version: 0.2.273-1
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Dockerfile

@@ -24,7 +24,7 @@ RUN echo "Building tags/${NODE_VERSION}..." \
 FROM ghcr.io/blinklabs-io/cardano-cli:10.12.0.0-1 AS cardano-cli
 FROM ghcr.io/blinklabs-io/cardano-configs:20251014-1 AS cardano-configs
 FROM ghcr.io/blinklabs-io/mithril-client:0.12.33-1 AS mithril-client
-FROM ghcr.io/blinklabs-io/mithril-signer:0.2.268-1 AS mithril-signer
+FROM ghcr.io/blinklabs-io/mithril-signer:0.2.276-1 AS mithril-signer
 FROM ghcr.io/blinklabs-io/nview:0.11.0 AS nview
 FROM ghcr.io/blinklabs-io/txtop:0.13.1 AS txtop