[dotnet] fix typo

Author: titusfortner

dotnet/private/merge_assemblies.bzl

@@ -41,7 +41,7 @@ def _merged_assembly_impl(ctx):
     ctx.actions.run(
         executable = ctx.executable.merge_tool,
         mnemonic = "MergeAssembly",
-        progress_message = "Merging assembiles into {}".format(output_assembly.path),
+        progress_message = "Merging assemblies into {}".format(output_assembly.path),
         arguments = args,
         inputs = ctx.attr.src_assembly.files,
         outputs = [output_assembly, output_pdb],