build(deps): bump github.com/sigstore/timestamp-authority

Bumps the actions group in /.github with 1 update: [github.com/sigstore/timestamp-authority](https://github.com/sigstore/timestamp-authority).


Updates `github.com/sigstore/timestamp-authority` from 1.2.3 to 1.2.4
- [Release notes](https://github.com/sigstore/timestamp-authority/releases)
- [Changelog](https://github.com/sigstore/timestamp-authority/blob/main/CHANGELOG.md)
- [Commits](sigstore/timestamp-authority@v1.2.3...v1.2.4)

---
updated-dependencies:
- dependency-name: github.com/sigstore/timestamp-authority
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: actions
...

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

.github/go.mod

@@ -1,11 +1,7 @@
 module sigstore/sigstore-python
 
 go 1.23
+toolchain go1.23.5
 
-require (
-    // We don't have a Go module here but this file is picked up by dependabot
-    // and this will automatically update the dependency when needed.
-
-    github.com/sigstore/timestamp-authority v1.2.3
-
-)
+// We don't have a Go module here but this file is picked up by dependabot
+// and this will automatically update the dependency when needed.