fix: use deno LTS in devcontainer

[tugrulates]

Bug

The current deno version installed in the devcontainer does not support the current deno.lock version (5).

deno task serve

error: Failed reading lockfile at '/workspaces/deno-docs/deno.lock'

Caused by:
    Unsupported lockfile version '5'. Try upgrading Deno or recreating the lockfile

deno —version

deno 2.0.4 (stable, release, x86_64-unknown-linux-gnu)
v8 12.9.202.13-rusty
typescript 5.6.2

Fix

Use the latest LTS deno version.

Testing

Tested on Codespaces.

• post create command succeeds
  • deno.lock does not change with deno install here
• deno task serve runs and the doc site works
• deno task test succeeds