Fix env var restoration on error path to prevent test pollution

[cderv]

When tests pass environment variables via TestContext.env, the quarto() function sets them globally with Deno.env.set() and restores the original values after execution. However, the restore code only runs on the success path — if await promise throws (e.g. a CommandError from a failed render, or Deno's exit sanitizer intercepting a Deno.exit() call inside the command), execution jumps to the catch block and the env vars are never restored.

In the sequential test runner (deno test with all files in one process), this means env vars from a failing test leak to all subsequent tests.

Fix

Move the env restoration into a finally block so it runs on both success and error paths.

Context

Discovered while reviewing #14241, which adds a test that sets QUARTO_PDF_STANDARD via TestContext.env. Same class of env pollution as #14218, though #14218 is a separate issue where crossref.ts sets env vars directly without any cleanup mechanism.

Related: #12621 (broader Deno.env cleanup effort)

[posit-snyk-bot]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues
✅	Licenses	0	0	0	0	0 issues

💻 Catch issues earlier using the plugins for VS Code, JetBrains IDEs, Visual Studio, and Eclipse.

[cscheid]

This is another instance of the class of bugs "we should set up env variables first and never touch them again". Not something we'll be able to fully fix before Quarto 2, and this is a good PR - I'm just pointing out the general principle.