Use sha256 to satisfy weak hash query. (#330)

CodeQL flags usage of md5 so switch to sha256 like used in the rest of
Triton.

Author: red1bluelost

backend/compiler.py

@@ -200,7 +200,7 @@ def __post_init__(self):
 
     def hash(self):
         key = '_'.join([f'{name}-{val}' for name, val in self.__dict__.items()])
-        return hashlib.md5(key.encode("utf-8")).hexdigest()
+        return hashlib.sha256(key.encode("utf-8")).hexdigest()
 
 
 class CPUBackend(BaseBackend):

backend/driver.py

@@ -269,7 +269,7 @@ def launch(
         kernel_name = kernel_metadata[6] # see pack_metadata in compiler.py
         src = launcher_src.replace(kernel_placeholder_name, kernel_name)
 
-        key = hashlib.md5(src.encode("utf-8") + kernel_obj).hexdigest()
+        key = hashlib.sha256(src.encode("utf-8") + kernel_obj).hexdigest()
         cache = get_cache_manager(key)
         name = "__triton_shared_ref_cpu_kernel_launcher"