test: Use byte unit 'M' for -maxuploadtarget functional test

test/functional/feature_maxuploadtarget.py

@@ -36,7 +36,7 @@ class MaxUploadTest(BitcoinTestFramework):
         self.setup_clean_chain = True
         self.num_nodes = 1
         self.extra_args = [[
-            "-maxuploadtarget=800",
+            "-maxuploadtarget=800M",
             "-acceptnonstdtxn=1",
         ]]
         self.supports_cli = False