chore(master): release 2.68.0

[github-actions]

🤖 I have created a release beep boop

2.68.0 (2026-05-17)

Features

• accept threadId on the submit reference object (b1b3dc7)
• add Workload Identity Federation for Gmail service accounts (1879c5a)
• revoke upstream OAuth2 grant on account delete via ?revoke=true (2a8c8fa)
• revoke upstream OAuth2 grant on account delete via ?revoke=true (15bc43a)

Bug Fixes

• flag WIF support in the gmailService form intro (61fab27)
• force-exit external-account-signer test to unblock CI (f4a1e4e)
• pkg config options must be a string array (6c4702d)
• prefer refresh token and skip gmailService when revoking on delete (e0dbea8)
• relax cross-folder assertion in Graph API parentFolderId test (770279d)

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