update-version.sh: update usage docs, other small changes

[jameslamb]

Contributes to #13

Some small updates to update-version.sh:

• adds docs on how to use --run-context (new as of the new RAPIDS branching strategy)
• makes some tests safer in the presence of set -u (to ensure informative errors are raised)
• updates shellcheck pre-commit hook to the latest version

Notes for Reviewers

How I tested this

git fetch upstream --tags
./ci/release/update-version.sh '26.06.00' --run-context=main
git grep -E '25\.|26\.2|26\.02|26\.4|26\.04'

[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: 332a2c8b-9060-4940-8413-4d1833963271

📥 Commits

Reviewing files that changed from the base of the PR and between ea0302b and 72a7559.

📒 Files selected for processing (2)

• .pre-commit-config.yaml
• ci/release/update-version.sh

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📝 Walkthrough

Summary by CodeRabbit

• Chores

  • Updated shellcheck-py hook version.

• Bug Fixes

  • Enhanced script robustness by improving handling of optional context inputs with safe parameter expansion and default values.
  • Added validation for run context values to ensure only valid options are accepted.
  • Improved error handling for unset variables in release scripts.

Walkthrough

The PR updates a pre-commit hook version and refactors a shell script to safely handle optional context inputs using parameter expansion, add default RUN_CONTEXT behavior, validate context values, and improve error handling.

Changes

Cohort / File(s)	Summary
Pre-commit configuration .pre-commit-config.yaml	Updated shellcheck-py hook version from v0.10.0.1 to v0.11.0.1.
Shell script improvements ci/release/update-version.sh	Introduced parameter expansion for CLI_RUN_CONTEXT and RAPIDS_RUN_CONTEXT variables; added default RUN_CONTEXT behavior (defaults to main); added validation to reject values other than main or release; improved usage documentation; updated NEXT_FULL_TAG existence check for graceful handling of unset variables.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title directly references the main file being modified (update-version.sh) and accurately describes the primary changes: documentation updates and other small improvements.
Description check	✅ Passed	The description is directly related to the changeset, explaining the purpose of updates to update-version.sh, the shellcheck hook version bump, and providing context through linked issues and test procedures.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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