fix(gcds-table): Update filter input label

[ethanWallace]

📝 Summary | Résumé

Update the filter input label available in the filter and sort dialog of gcds-table to provide clearer instructions to the user.

🧩 Related Issues | Cartes liées

• Issue [A11y] Filter field lacks clear labeling and placeholder text design-gc-conception#2541

🧪 Test instructions | Instructions pour tester la modification

2. Validate the change

• Checkout this branch
• Run npm run start
• Navigate down to table example
• Open the Filter and sort dialog
• Observe the label is now "Filter by keyword" in English and "Filtrer par mot-clé" in French

✍️ Author checklist | Liste de vérification de l'auteur

Choose one:

• This PR is a patch (use fix:)
• This PR introduces a minor change (use feat:)
• This PR introduces breaking changes to the API (use feat!:)
• This PR does not introduce changes that need to be published on NPM (use chore:, docs:, ci:)

Breaking changes flag:

• This PR does not break existing functionality. I have completely tested the functionality of these changes.
• This PR does not introduce any changes to component names, properties, values, or behaviour.
• If this PR introduces API or behaviour changes, backwards compatibility has been implemented and documented under Impact and Risks.
• If this PR introduces a breaking change, release notes and versioning have been prepared.

Ready for review: (all items must be checked)

• I have tested the English and French versions of the changes, and can verify that all content is accurate and properly displayed in both languages.
• I have tested these changes on mobile viewports.
• I have tested these changes across multiple supported browsers.
• I have checked accessiblity and ensured all accessiblity tests pass.
• I have added tests for added functionality or changed existing tests, as needed.
• I have added or updated documentation, if needed.
• For visual or design-affecting changes, I have posted in dev-design slack channel.
• Visual or content changes remain aligned with design tokens and component API standards.
• Test instructions are clear and reproducible.

🧐 Reviewer checklist | Liste de vérification du réviseur

Developer checklist

For PRs that are complex, in lieu of a simple approval or an "LGTM" ✅, paste the following info with your approval:

• I have tested the changes and functionality using the test instructions.
• I have confirmed test coverage is adequate.
• I have reviewed the code for clarity, maintainability and potential issues.

Design checklist (if needed)

For designers, include the following info with your approval:

• I have tested the changes and functionality using the test instructions.
• The changes meet design expectations and align with the design system.
• Any design inconsistencies have been raised on slack or tracked via an issue.

Content checklist (if needed)

For content, include the following info with your approval:

• I understand the context and intent of the content changes.
• I have reviewed all content for clarity, readability, and tone.
• I have reviewed English and French content for accuracy and parity.

[EliseKa]

LGTM