gdb/python: fix memory leak of gdb.Color objects

I noticed that this commit:

  commit 6447969d0a
  Date:   Sat Oct 5 22:27:44 2024 +0300

      Add an option with a color type.

has an unnecessary `Py_INCREF (self);` in gdb.Color.__init__.  This
means that the reference count on all gdb.Color objects (that pass
through __init__) will be +1 from where they should normally be, and
this will stop the gdb.Color objects from being deallocated.

Fix by removing the Py_INCREF call.

Add a test which exposes the memory leak.

Approved-By: Tom Tromey <tom@tromey.com>

gdb/python/py-color.c

@@ -256,7 +256,6 @@ colorpy_init (PyObject *self, PyObject *args, PyObject *kwds)
       return gdbpy_handle_gdb_exception (-1, except);
     }
 
-  Py_INCREF (self);
   return 0;
 }
 

gdb/testsuite/gdb.python/py-color-leak.exp

@@ -0,0 +1,28 @@
+# Copyright (C) 2025 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# This file is part of the GDB testsuite.  It checks for memory leaks
+# associated with allocating gdb.Color objects.
+
+load_lib gdb-python.exp
+
+require allow_python_tests
+
+standard_testfile
+
+clean_restart
+
+gdb_py_run_memory_leak_test ${srcdir}/${subdir}/${testfile}.py \
+    "gdb.Color object deallocates correctly"

gdb/testsuite/gdb.python/py-color-leak.py

@@ -0,0 +1,31 @@
+# Copyright (C) 2025 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import gdb_leak_detector
+
+
+class color_leak_detector(gdb_leak_detector.gdb_leak_detector):
+    def __init__(self):
+        super().__init__(__file__)
+        self.color = None
+
+    def allocate(self):
+        self.color = gdb.Color("red")
+
+    def deallocate(self):
+        self.color = None
+
+
+color_leak_detector().run()