♻️ Prevent unit tests from running concurrently

The way the testing classes are built with the singletons currently
prevents various test structs from being run at the same time.

I've adjusted the tests in the PHP Monitor EAP test configuration so
that they are not executed concurrently. This does slow down the test
suite but prevents odd crashes from individual tests interfering with
other tests.

It's not an ideal solution and I would like to address this in the
future, but I suspect this will be rather cumbersome. Since the app
does not actually suffer from this particular issue, this is something
worth investigating later.

tests/unit/SwiftTestMigrated/Parsers/PhpConfigurationFileTest.swift

@@ -9,13 +9,14 @@
 import Testing
 import Foundation
 
+@Suite(.serialized)
 class PhpConfigurationFileTest {
-
     static var phpIniFileUrl: URL {
         return TestBundle.url(forResource: "php", withExtension: "ini")!
     }
 
     @Test func can_load_extension() throws {
+        ActiveFileSystem.useSystem()
         let iniFile = PhpConfigurationFile.from(filePath: Self.phpIniFileUrl.path)
 
         #expect(iniFile != nil)
@@ -23,6 +24,7 @@ class PhpConfigurationFileTest {
     }
 
     @Test func can_check_key_existence() throws {
+        print(Self.phpIniFileUrl.path)
         let iniFile = PhpConfigurationFile.from(filePath: Self.phpIniFileUrl.path)!
 
         #expect(iniFile.has(key: "error_reporting"))