Revert to the previous quoting behaviour for environment option

unit_test/options_test.py

@@ -62,7 +62,7 @@ test_command: 'pyproject'
 
     default_build_options = options.build_options(identifier=None)
 
-    assert default_build_options.environment == parse_environment("FOO=BAR")
+    assert default_build_options.environment == parse_environment('FOO="BAR"')
 
     all_pinned_container_images = _get_pinned_container_images()
     pinned_x86_64_container_image = all_pinned_container_images["x86_64"]
@@ -122,14 +122,19 @@ def test_passthrough_evil(tmp_path, monkeypatch, env_var_value):
     assert parsed_environment.as_dictionary(prev_environment={}) == {"ENV_VAR": env_var_value}
 
 
+xfail_env_parse = pytest.mark.xfail(
+    raises=SystemExit, reason="until we can figure out the right way to quote these values"
+)
+
+
 @pytest.mark.parametrize(
     "env_var_value",
     [
         "normal value",
-        '"value wrapped in quotes"',
-        'an unclosed double-quote: "',
+        pytest.param('"value wrapped in quotes"', marks=[xfail_env_parse]),
+        pytest.param('an unclosed double-quote: "', marks=[xfail_env_parse]),
         "string\nwith\ncarriage\nreturns\n",
-        "a trailing backslash \\",
+        pytest.param("a trailing backslash \\", marks=[xfail_env_parse]),
     ],
 )
 def test_toml_environment_evil(tmp_path, monkeypatch, env_var_value):
@@ -163,6 +168,9 @@ def test_toml_environment_evil(tmp_path, monkeypatch, env_var_value):
         ('TEST_VAR="before:$PARAM:after"', "before:spam:after"),
         # env var extension with spaces
         ('TEST_VAR="before $PARAM after"', "before spam after"),
+        # literal $ - this test is just for reference, I'm not sure if this
+        # syntax will work if we change the TOML quoting behaviour
+        (r'TEST_VAR="before\\$after"', "before$after"),
     ],
 )
 def test_toml_environment_quoting(tmp_path: Path, toml_assignment, result_value):