build: Fix CMake build by adding missing source file (#1239)

Follow-up to 63cfcb9

Author: kateinoigakukun

Sources/FoundationEssentials/Formatting/CMakeLists.txt

@@ -15,6 +15,7 @@
 target_sources(FoundationEssentials PRIVATE
     BinaryInteger+NumericStringRepresentation.swift
     Date+ISO8601FormatStyle.swift
+    DateComponents+ISO8601FormatStyle.swift
     DiscreteFormatStyle.swift
     FormatParsingUtilities.swift
     FormatStyle.swift