fix: culture must be the default culture provided by .NET (#278)

Before the fix, local computer settings changes could affect the culture, decreasing the library's portability.

Expressif.Testing/Predicates/Text/MatchingTest.cs

@@ -189,6 +189,17 @@ public void MatchesDateTime_InvariantCultureTimeOnly_Valid()
     public void MatchesTime_InvariantCulture_Success(object? value, bool expected)
         => Assert.That(new MatchesTime().Evaluate(value), Is.EqualTo(expected));
 
+    [Test]
+    [TestCase("25/12/2025 10:01:55", false)]
+    public void MatchesDateTime_AmericanCulture_Fail(object? value, bool expected)
+        => Assert.That(new MatchesDateTime(() => "en-US").Evaluate(value), Is.EqualTo(expected));
+
+    [Test]
+    [TestCase("25/12/2025 10:01:55", true)]
+    public void MatchesDateTime_FrenchCulture_Success(object? value, bool expected)
+        => Assert.That(new MatchesDateTime(() => "fr-FR").Evaluate(value), Is.EqualTo(expected));
+
+
     [Test]
     [TestCase("2022-11-02", false)]
     [TestCase("2022-11-02 13:57:00", false)]

Expressif/Predicates/Text/Matching.cs

@@ -23,7 +23,7 @@ public BaseTextPredicateMatching(Func<string> culture)
     protected virtual CultureInfo GetCulture(string culture)
     {
         if (!string.IsNullOrEmpty(culture))
-            return (new CultureInfo(culture).Clone() as CultureInfo)!;
+            return new CultureInfo(culture, false);
 
         var invariantCulture = (CultureInfo.InvariantCulture.Clone() as CultureInfo)!;
         invariantCulture.DateTimeFormat.ShortDatePattern = "yyyy/MM/dd";