build: Use the shared crossplane cachix cache in nix.sh

[adamwg]

Description of your changes

Our CI is already pushing to the org-wide cachix cache called crossplane. Update nix.sh to use this cache rather than the non-existent one called crossplane-cli.

I have:

• Read and followed Crossplane's contribution process.
• Run ./nix.sh flake check to ensure this PR is ready for review.
  - [ ] Added or updated unit tests.
  - [ ] Linked a PR or a docs tracking issue to document this change.
  - [ ] Added backport release-x.y labels to auto-backport this PR.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: a26efb8d-62ac-47a3-a6d9-75fcca7646dd

📥 Commits

Reviewing files that changed from the base of the PR and between bc59509 and e0077c7.

📒 Files selected for processing (1)

• nix.sh

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📝 Walkthrough

Walkthrough

The PR updates the Nix binary cache configuration in the Docker container setup to use crossplane.cachix.org instead of crossplane-cli.cachix.org, including the corresponding public key update for cache authentication.

Changes

Cachix Binary Cache Configuration

Layer / File(s)	Summary
Nix binary cache endpoint and keys update nix.sh	The Cachix substituter URL in extra-substituters and the corresponding trusted public key in extra-trusted-public-keys are updated from crossplane-cli.cachix.org to crossplane.cachix.org.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

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Important

Pre-merge checks failed

Please resolve all errors before merging. Addressing warnings is optional.

❌ Failed checks (1 error)

Check name	Status	Explanation	Resolution
Breaking Changes	❌ Error	Files under apis/** and cmd/** add new required public fields (e.g., Project struct in project_types.go with required Spec field) without a 'breaking-change' label.	Add 'breaking-change' label to the PR, or clarify the scope of the check to exclude initial repository setup commits with only newly added files.

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and descriptively summarizes the main change: updating nix.sh to use the shared crossplane cachix cache instead of the non-existent one.
Description check	✅ Passed	The description is directly related to the changeset, explaining the motivation (CI already pushes to org-wide cache) and the specific update being made (switching from crossplane-cli to crossplane cache).
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Feature Gate Requirement	✅ Passed	PR updates nix.sh Cachix cache configuration from non-existent to organization-wide cache. This is a build infrastructure fix, not a new experimental feature requiring feature gates.

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