unordered-containers: Support ghc-9.12

The `template-haskell` upper bound needs bumping.

After doing that, and adding a `cabal.project` file containing:
```
packages:
  . 

tests: True

allow-newer:
  , hashable:base
  , primitive:base
  , splitmix:base
  , ChasingBottoms:base
```
it builds and all tests pass.