Swift: Special case the xcode-fails-spm-works test results on macOS 26

macOS 26 comes with Xcode 26, which does not call the compiler on the file
with the `#error` diagnostic directive.

Author: jketema

swift/ql/integration-tests/autobuilder/xcode-fails-spm-works/Files.macos_26.expected

@@ -0,0 +1,3 @@
+| Package.swift:0:0:0:0 | Package.swift |
+| Sources/hello-world/hello_world.swift:0:0:0:0 | Sources/hello-world/hello_world.swift |
+| file://:0:0:0:0 |  |

swift/ql/integration-tests/autobuilder/xcode-fails-spm-works/test.py

@@ -3,6 +3,7 @@
 
 
 @runs_on.macos
-@pytest.mark.ql_test("DB-CHECK", xfail=True)
+@pytest.mark.ql_test("DB-CHECK", xfail=not runs_on.macos_26)
+@pytest.mark.ql_test("*", expected=f"{'.macos_26' if runs_on.macos_26 else ''}.expected")
 def test(codeql, swift):
     codeql.database.create()