feat(spec): add Icelandic locale support (lingodotdev#995)

* feat(spec): add Icelandic locale support

- Add is (Icelandic) locale code with is-IS regional variant to localeMap
- Create changeset documenting the minor version bump
- Resolves lingodotdev#994

Co-Authored-By: Max Prilutskiy <maks.prilutskiy@gmail.com>

* fix(changeset): change version bump from minor to patch

- Address feedback from @maxprilutskiy
- Adding new locale support is more appropriate as patch-level change

Co-Authored-By: Max Prilutskiy <maks.prilutskiy@gmail.com>

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: Max Prilutskiy <maks.prilutskiy@gmail.com>

Author: devin-ai-integration[bot]

.changeset/soft-seals-doubt.md

@@ -0,0 +1,5 @@
+---
+"@lingo.dev/_spec": patch
+---
+
+Add Icelandic (is) locale support with is-IS regional variant

packages/spec/src/locales.ts

@@ -127,6 +127,7 @@ const localeMap = {
   pl: ["pl-PL"],
   // Indonesian (Indonesia)
   id: ["id-ID"],
+  is: ["is-IS"],
   // Malay (Malaysia)
   ms: ["ms-MY"],
   // Finnish (Finland)