[clang] [Serialization] Fix lazy template loading (PR #133057)

[Maksim Ivanov via cfe-commits]

emaxx-google wrote:

Here's a new reproducer, this time verifying that a semi-fresh tip-of-the-tree doesn't trigger the same error: https://pastebin.com/7tYfjazz. Apologies for the delay.

https://github.com/llvm/llvm-project/pull/133057