chore: bump Dagger to 0.21.8

[jpmcb]

Bump Dagger engine to v0.21.8 (latest, 2026-07-29) and dagger/dagger-for-github to v8.4.1.

[greptile-apps]

Greptile Summary

The PR consistently upgrades the Dagger engine and GitHub Action used by CI, pull-request, nightly, and release automation.

• Updates workflow-installed Dagger from 0.20.8 to 0.21.8.
• Updates dagger/dagger-for-github from v8.2.0 to v8.4.1.
• Aligns dagger.json with engine v0.21.8.

Confidence Score: 5/5

The PR appears safe to merge because the workflow CLI versions, action versions, and module engine version are updated consistently.

No concrete changed-code-triggered failure remains; all workflows install Dagger 0.21.8 through the updated action, and dagger.json requests the matching engine version.

Important Files Changed

Filename	Overview
.github/workflows/ci.yaml	Updates the Dagger CLI and action versions while preserving explicit, matching version wiring for Linux builds.
.github/workflows/cut-release.yaml	Updates the Dagger installation used by release creation without changing release behavior.
.github/workflows/nightly.yaml	Consistently updates both Dagger installation steps used by nightly build and upload jobs.
.github/workflows/pr.yaml	Consistently updates both Dagger installation steps used by pull-request checks.
.github/workflows/release.yaml	Consistently updates the Dagger installations used by release build and upload jobs.
dagger.json	Updates the required Dagger engine version to match the workflow-installed CLI.

_{Reviews (1): Last reviewed commit: "chore: bump Dagger to 0.21.8" | Re-trigger Greptile}