ci: pin Lint workflow to Deno v2.x stable

[fibibot]

Summary

The lint and link check workflow has been failing on every recent PR
with an MDX rendering error in /styleguide/typography.mdx:

TypeError: Cannot resolve module "lume/jsx-runtime":
relative URL with a cannot-be-a-base base
  at MDXEngine.render (https://cdn.jsdelivr.net/gh/lumeland/lume@3.1.2/plugins/mdx.ts:96:21)

Root cause

.github/workflows/lint.yml sets deno-version: canary. The lume MDX
plugin compiles MDX to JS, wraps the output in URL.createObjectURL(new Blob(...)),
and dynamic-imports the resulting blob: URL. The compiled output references
"lume/jsx-runtime", which is supposed to be resolved via the import map in
deno.json:

"lume/jsx-runtime": "https://cdn.jsdelivr.net/gh/oscarotero/ssx@0.1.14/jsx-runtime.ts"

A recent canary regression broke bare-specifier resolution when the importer
is a blob: URL — Deno now tries to resolve "lume/jsx-runtime" as a relative
URL against the blob: referrer (which is a cannot-be-a-base URL) and errors out before the import map is consulted.

The same build succeeds locally on deno 2.7.14 (stable). The deploy/deno/docs
preview build (which doesn't use canary) has been green throughout.

Fix

Pin to the v2.x stable channel. This keeps automatic stable-version uptake
without exposure to unreleased regressions. Drop-in change — no other workflow
uses canary.

When canary stabilises this regression (likely in the next stable bump that
includes the underlying URL resolver change), v2.x will pick it up naturally.

cc @bartlomieju — fixes the CI breakage you flagged on #3114.

Closes bartlomieju/orchid-inbox#57

Test plan

• CI's lint and link check passes on this PR (was failing on every recent PR including docs: troubleshoot "command not found" after install #3114, docs: document DENO_INSTALL env var on installation page #3112, docs: clarify /deploy/kv/node/ is for Deploy Classic #3110, etc.).
• After merge, re-runs on those PRs succeed.