fix(ci): skip vscode publish steps when registry token is missing

[jimisola]

Summary

• HaaLeo/publish-vscode-extension@v2 treats an empty pat as "not supplied" and errors hard, even though both secrets (OPEN_VSX_TOKEN, VSCE_PAT) are declared required: false
• Adds a Check token availability step that writes boolean outputs by inspecting the secrets via env vars
• Gates each publish step on both the registry input and the token being present, so the job succeeds gracefully when a secret is not configured

Test plan

• Verify the failing run on reqstool-vscode would now skip Publish to Open VSX Registry instead of erroring
• Confirm a run with both tokens set still publishes to both registries

[jimisola]

Closing — the build should fail when a registry token is missing. The fix is to add the missing secret to the repo.