vendor.gowin: do not overwrite synthesis JSON with P&R result.

Author: whitequark

amaranth/vendor/gowin.py

@@ -223,7 +223,7 @@ def _osc_div(self):
             read_ilang {{name}}.il
             delete w:$verilog_initial_trigger
             {{get_override("script_after_read")|default("# (script_after_read placeholder)")}}
-            synth_gowin {{get_override("synth_opts")|options}} -top {{name}} -json {{name}}.json
+            synth_gowin {{get_override("synth_opts")|options}} -top {{name}} -json {{name}}.syn.json
             {{get_override("script_after_synth")|default("# (script_after_synth placeholder)")}}
         """,
     }
@@ -242,16 +242,16 @@ def _osc_div(self):
             --log {{name}}.tim
             --device {{platform.part}}
             --family {{platform._chipdb_device}}
-            --json {{name}}.json
+            --json {{name}}.syn.json
             --cst {{name}}.cst
-            --write {{name}}.json
+            --write {{name}}.pnr.json
         """,
         r"""
         {{invoke_tool("gowin_pack")}}
             -d {{platform._chipdb_device}}
             -o {{name}}.fs
             {{get_override("gowin_pack_opts")|options}}
-            {{name}}.json
+            {{name}}.pnr.json
         """
     ]