fix: remove unwanted doctypes from svg sprite (#229)

# Changes

- Adds an icon that is known to have a doctype definition in it
- Adds the flag to strip doctype in svg-sprite


# How to test

1. Run `npm run build && npm run lint` to see no errors regarding
`doctype`
2. Verify that there is only one `doctype` in any html file.
3. Verify that there was a `doctype` in the `close.svg` file.

# Checklist

- [X] I have performed a self-review of my own code
- [X] I have made sure that my PR is easy to review (not too big,
includes comments)
- [ ] ~I have made updated relevant documentation files (in project
README, docs/, etc)~
- [ ] ~I have added a decision log entry if the change affects the
architecture or changes a significant technology~
- [X] I have notified a reviewer

<!-- Please strike through and check off all items that do not apply
(rather than removing them) -->

package.json

@@ -27,7 +27,7 @@
     "prep:download-redirects": "jiti scripts/download-redirects.ts",
     "prep:download-site-data": "jiti scripts/download-site-data.ts",
     "prep:download-translations": "jiti scripts/download-translations.ts",
-    "prep:icons": "svg-sprite --symbol --symbol-dest='src/assets' --symbol-sprite=icon-sprite.svg src/assets/icons/*.svg && jiti scripts/icon-types.ts",
+    "prep:icons": "svg-sprite --svg-doctype=false --symbol --symbol-dest='src/assets' --symbol-sprite=icon-sprite.svg src/assets/icons/*.svg && jiti scripts/icon-types.ts",
     "preview": "wrangler pages dev ./dist",
     "lint": "run-s lint:* --print-label",
     "lint:astro": "astro check",