Mark as compatible with MemPool 0.4

Exclusive compatibility with MemPool 0.3 was restricting DaggerGPU from being used with Dagger 0.16 in practice. Add 0.4 to the list of acceptable versions of MemPool.

Author: EricHallahan

Project.toml

@@ -16,7 +16,7 @@ UUIDs = "cf7118a7-6976-5b1a-9a39-7adc72f591a4"
 Adapt = "1, 2, 3"
 Dagger = "0.13.3, 0.14, 0.15, 0.16"
 KernelAbstractions = "0.5, 0.6, 0.7"
-MemPool = "0.3"
+MemPool = "0.3, 0.4"
 Requires = "1"
 julia = "1"