Raise heap size of memory tests from 8M to 16M (fixes #8029)

There appears to be a small regression in heap usage with GHC 9.2.1.
This raises the limit to accommodate that, and give a bit of a buffer.
Compare analysis at #8029.

cabal-install/cabal-install.cabal

@@ -339,7 +339,7 @@ Test-Suite memory-usage-tests
   hs-source-dirs: tests
   default-language: Haskell2010
 
-  ghc-options: -threaded -rtsopts "-with-rtsopts=-M8M -K1K"
+  ghc-options: -threaded -rtsopts "-with-rtsopts=-M16M -K1K"
 
   other-modules:
     UnitTests.Distribution.Solver.Modular.DSL