refactor(Modal): adjust header border-color to `gray/200`

[cf-remylenoir]

Purpose of PR

Ensure design <-> code is aligned.

Our modal header border color is set to gray/300 in the code vs gray/200 in the design.

PR Checklist

• [x] I have read the relevant readme.md file(s)
• [x] All commits follow our Git commit message convention
• [x] Tests are added/updated/not required
• [x] Tests are passing
• [x] Storybook stories are added/updated/not required
• [x] Usage notes are added/updated/not required
• [x] Has been tested based on Contentful's browser support
• [x] Doesn't contain any sensitive information

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Name	Status	Preview	Updated (UTC)
forma-36	✅ Ready (Inspect)	Visit Preview	Jul 30, 2024 8:02am

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 3daf739332ba497c5ffb35ed23994b46cc4491bc

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 36 packages

| Name | Type | | ---------------------------- | ----- | | @contentful/f36-modal | Patch | | @contentful/f36-accordion | Patch | | @contentful/f36-asset | Patch | | @contentful/f36-autocomplete | Patch | | @contentful/f36-badge | Patch | | @contentful/f36-button | Patch | | @contentful/f36-card | Patch | | @contentful/f36-collapse | Patch | | @contentful/f36-copybutton | Patch | | @contentful/f36-core | Patch | | @contentful/f36-datetime | Patch | | @contentful/f36-datepicker | Patch | | @contentful/f36-drag-handle | Patch | | @contentful/f36-entity-list | Patch | | @contentful/f36-empty-state | Patch | | @contentful/f36-forms | Patch | | @contentful/f36-icon | Patch | | @contentful/f36-header | Patch | | @contentful/f36-list | Patch | | @contentful/f36-menu | Patch | | @contentful/f36-navbar | Patch | | @contentful/f36-note | Patch | | @contentful/f36-notification | Patch | | @contentful/f36-pagination | Patch | | @contentful/f36-pill | Patch | | @contentful/f36-popover | Patch | | @contentful/f36-skeleton | Patch | | @contentful/f36-spinner | Patch | | @contentful/f36-table | Patch | | @contentful/f36-tabs | Patch | | @contentful/f36-text-link | Patch | | @contentful/f36-tooltip | Patch | | @contentful/f36-typography | Patch | | @contentful/f36-components | Patch | | @contentful/f36-image | Patch | | @contentful/f36-avatar | Patch |

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[github-actions[bot]]

size-limit report 📦

Path	Size	Loading time (3g)	Running time (snapdragon)	Total time
CommonJS	136.69 KB (+0.01% 🔺)	2.8 s (+0.01% 🔺)	590 ms (+13.45% 🔺)	3.4 s
Module	132.95 KB (+0.01% 🔺)	2.7 s (+0.01% 🔺)	846 ms (+27.9% 🔺)	3.6 s