[3.15] gh-154279: Skip readline completion tests that fail on DragonFly and illumos (GH-154280) (GH-154282)

They are already skipped on FreeBSD, where a backspace does not remove
the auto-indentation.  The same happens on DragonFly and illumos.
(cherry picked from commit e81f190)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 3 people

Lib/test/test_pdb.py

@@ -5167,8 +5167,9 @@ def f():
 
         self.assertIn('I love Python', output)
 
-    @unittest.skipIf(sys.platform.startswith('freebsd'),
-                     '\\x08 is not interpreted as backspace on FreeBSD')
+    @unittest.skipIf(sys.platform.startswith(('freebsd', 'dragonfly', 'sunos')),
+                     '\\x08 does not remove the auto-indentation with '
+                     'GNU readline on this platform')
     def test_multiline_auto_indent(self):
         script = textwrap.dedent("""
             import pdb; pdb.Pdb().set_trace()
@@ -5207,8 +5208,9 @@ def test_multiline_completion(self):
 
         self.assertIn('42', output)
 
-    @unittest.skipIf(sys.platform.startswith('freebsd'),
-                     '\\x08 is not interpreted as backspace on FreeBSD')
+    @unittest.skipIf(sys.platform.startswith(('freebsd', 'dragonfly', 'sunos')),
+                     '\\x08 does not remove the auto-indentation with '
+                     'GNU readline on this platform')
     def test_multiline_indent_completion(self):
         script = textwrap.dedent("""
             import pdb; pdb.Pdb().set_trace()

Lib/test/test_sqlite3/test_cli.py

@@ -381,10 +381,10 @@ def test_complete_schemata(self):
         self.assertIn("main", candidates)
         self.assertIn("temp", candidates)
 
-    @unittest.skipIf(sys.platform.startswith("freebsd"),
+    @unittest.skipIf(sys.platform.startswith(("freebsd", "dragonfly", "sunos")),
                     "Two actual tabs are inserted when there are no matching"
                     " completions in the pseudo-terminal opened by run_pty()"
-                    " on FreeBSD")
+                    " on this platform")
     def test_complete_no_match(self):
         input_ = b"xyzzy\t\t\b\b\b\b\b\b\b.quit\n"
         # Set NO_COLOR to disable coloring for self.PS1.