[libs][Unix] Fix UTC alias lookup (#88641)

Author: RenderMichael

src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.Unix.cs

@@ -33,8 +33,8 @@ private static bool IsUtcAlias (string id)
                 case 69: // e
                 case 101: // E
                     return string.Equals(id, "Etc/UTC", StringComparison.OrdinalIgnoreCase) ||
+                           string.Equals(id, "Etc/UCT", StringComparison.OrdinalIgnoreCase) ||
                            string.Equals(id, "Etc/Universal", StringComparison.OrdinalIgnoreCase) ||
-                           string.Equals(id, "Etc/UTC", StringComparison.OrdinalIgnoreCase) ||
                            string.Equals(id, "Etc/Zulu", StringComparison.OrdinalIgnoreCase);
                 case 85: // u
                 case 117: // U

src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs

@@ -2334,6 +2334,14 @@ public static IEnumerable<object[]> SystemTimeZonesTestData()
                         yield return new object[] { tz };
                     }
                 }
+
+                if (!PlatformDetection.IsBrowser)
+                {
+                    foreach (string alias in s_UtcAliases)
+                    {
+                        yield return new object[] { TimeZoneInfo.FindSystemTimeZoneById(alias) };
+                    }
+                }
             }
         }
 
@@ -2424,6 +2432,20 @@ public static void TimeZoneDisplayNames_Unix(TimeZoneInfo timeZone)
             }
         }
 
+        [Fact]
+        [PlatformSpecific(~TestPlatforms.Windows & ~TestPlatforms.Browser)]
+        public static void UtcAliases_MapToUtc()
+        {
+            TimeZoneInfo.AdjustmentRule[] expectedAdjustmentRules = TimeZoneInfo.Utc.GetAdjustmentRules();
+
+            foreach (var alias in s_UtcAliases)
+            {
+                TimeZoneInfo actualUtc = TimeZoneInfo.FindSystemTimeZoneById(alias);
+                Assert.Equal(TimeZoneInfo.Utc.BaseUtcOffset, actualUtc.BaseUtcOffset);
+                Assert.Equal(expectedAdjustmentRules, actualUtc.GetAdjustmentRules());
+            }
+        }
+
         [ActiveIssue("https://github.com/dotnet/runtime/issues/19794", TestPlatforms.AnyUnix)]
         [Theory]
         [MemberData(nameof(SystemTimeZonesTestData))]