gdb: run black code formatter on gdbarch_components.py

The following commit changed gdbarch_components.py but failed to
format it with black:

  commit cf141dd8cc
  Date:   Wed Feb 22 12:15:34 2023 +0000

      gdb: fix reg corruption from displaced stepping on amd64

This commit just runs black on the file and commits the result.

The change is just the addition of an extra "," -- there will be no
change to the generated source files after this commit.

There will be no user visible changes after this commit.

gdb/gdbarch_components.py

@@ -1804,7 +1804,7 @@ see the comments in infrun.c.
         ("CORE_ADDR", "from"),
         ("CORE_ADDR", "to"),
         ("struct regcache *", "regs"),
-        ("bool", "completed_p")
+        ("bool", "completed_p"),
     ],
     predicate=False,
     predefault="NULL",