United States - Add Truman Day and Lincoln's Birthday (#742)

Author: tinohager

src/Nager.Date/HolidayProviders/UnitedStatesHolidayProvider.cs

@@ -137,6 +137,14 @@ protected override IEnumerable<HolidaySpecification> GetHolidaySpecifications(in
                     ObservedRuleSet = observedRuleSet
                 },
                 new HolidaySpecification
+                {
+                    Date = new DateTime(year, 5, 8),
+                    EnglishName = "Truman Day",
+                    LocalName = "Truman Day",
+                    HolidayTypes = HolidayTypes.Authorities | HolidayTypes.School,
+                    SubdivisionCodes = ["US-MO"]
+                },
+                new HolidaySpecification
                 {
                     Date = firstMondayInSeptember,
                     EnglishName = "Labor Day",
@@ -180,10 +188,23 @@ protected override IEnumerable<HolidaySpecification> GetHolidaySpecifications(in
 
             holidaySpecifications.AddIfNotNull(this.JuneteenthNationalIndependenceDay(year, observedRuleSet));
             holidaySpecifications.AddIfNotNull(this.IndigenousPeoplesDay(year));
+            holidaySpecifications.AddIfNotNull(this.LincolnsBirthday(year));
 
             return holidaySpecifications;
         }
 
+        private HolidaySpecification? LincolnsBirthday(int year)
+        {
+            return new HolidaySpecification
+            {
+                Date = new DateTime(year, 2, 12),
+                EnglishName = "Lincoln's Birthday",
+                LocalName = "Lincoln's Birthday",
+                HolidayTypes = HolidayTypes.Observance,
+                SubdivisionCodes = ["US-CA", "US-CT", "US-IL", "US-IN", "US-KY", "US-MI", "US-NY", "US-MO", "US-OH"],
+            };
+        }
+
         private HolidaySpecification? JuneteenthNationalIndependenceDay(
             int year,
             ObservedRuleSet observedRuleSet)