No. Whonix doesn’t stop the upgrade. See this thread on what was actually done, not done.
Whonix doesn’t interfere with package upgrades from Debian so package security support is same Debian and for other practical reasons, Focus on low-effort maintainability, not sustainable to fork/security support Thunderbird at Whonix project level.
Unspecific to Whonix. Same as Debian. Self Support First Policy for Whonix applies.