build(deps): bump the ci group across 1 directory with 2 updates

Bumps the ci group with 2 updates in the / directory: [sigstore/cosign-installer](https://github.com/sigstore/cosign-installer) and [slsa-framework/slsa-github-generator](https://github.com/slsa-framework/slsa-github-generator).


Updates `sigstore/cosign-installer` from 3.7.0 to 3.8.1
- [Release notes](https://github.com/sigstore/cosign-installer/releases)
- [Commits](https://github.com/sigstore/cosign-installer/compare/v3.7.0...v3.8.1)

Updates `slsa-framework/slsa-github-generator` from 2.0.0 to 2.1.0
- [Release notes](https://github.com/slsa-framework/slsa-github-generator/releases)
- [Changelog](https://github.com/slsa-framework/slsa-github-generator/blob/main/CHANGELOG.md)
- [Commits](https://github.com/slsa-framework/slsa-github-generator/compare/v2.0.0...v2.1.0)

---
updated-dependencies:
- dependency-name: sigstore/cosign-installer
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: ci
- dependency-name: slsa-framework/slsa-github-generator
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: ci
...

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

.github/workflows/push-ld.yml

@@ -17,7 +17,7 @@ jobs:
       packages: write
     steps:
       - uses: actions/checkout@v4
-      - uses: sigstore/cosign-installer@v3.7.0
+      - uses: sigstore/cosign-installer@v3.8.1
       - name: Prepare
         id: prep
         run: |

.github/workflows/release.yml

@@ -33,7 +33,7 @@ jobs:
         with:
           go-version: 1.24.x
       - uses: fluxcd/flux2/action@main
-      - uses: sigstore/cosign-installer@v3.7.0
+      - uses: sigstore/cosign-installer@v3.8.1
       - name: Prepare
         id: prep
         run: |
@@ -146,7 +146,7 @@ jobs:
       actions: read # for detecting the Github Actions environment.
       id-token: write # for creating OIDC tokens for signing.
       contents: write # for uploading attestations to GitHub releases.
-    uses: slsa-framework/slsa-github-generator/.github/workflows/generator_generic_slsa3.yml@v2.0.0
+    uses: slsa-framework/slsa-github-generator/.github/workflows/generator_generic_slsa3.yml@v2.1.0
     with:
       provenance-name: "provenance.intoto.jsonl"
       base64-subjects: "${{ needs.release-flagger.outputs.hashes }}"