Merge pull request #70726 from jmschonfeld/undeprecate-iscontiguousascii

Un-deprecate _StringGuts._isContiguousASCII

Author: jmschonfeld

stdlib/public/core/StringGuts.swift

@@ -402,7 +402,6 @@ extension _StringGuts {
 
 // Old SPI(corelibs-foundation)
 extension _StringGuts {
-  @available(*, deprecated)
   public // SPI(corelibs-foundation)
   var _isContiguousASCII: Bool {
     return !isSmall && isFastUTF8 && isASCII