[Tests][Add] Support for the nightly image

- It defines KICAD_PATH pointing to the nightly dir

tests/test_plot/kiconf_init.py

@@ -73,8 +73,13 @@ def do_init():
 
 if args.patch_get_path:
     with context.cover_it(cov):
+        old = os.environ.get('KICAD_PATH')
+        if old:
+            del os.environ['KICAD_PATH']
         with patch("sysconfig.get_path", lambda a, b=None: ''):
             do_init()
+        if old:
+            os.environ['KICAD_PATH'] = old
 else:
     with context.cover_it(cov):
         do_init()

tests/test_plot/test_kicad_config_errors.py

@@ -92,7 +92,8 @@ def test_kicad_conf_guess_libs(monkeypatch):
         name = "KICAD6_SYMBOL_DIR"
     else:
         name = "KICAD_SYMBOL_DIR"
-    assert 'Using {}="/usr/share/kicad/'.format(name) in res, res
+    assert ('Using {}="/usr/share/kicad/'.format(name) in res or
+            'Using {}="/usr/share/kicad-nightly/'.format(name) in res), res
 
 
 def test_kicad_conf_lib_env(monkeypatch):