Update SecureString.xml (#7344)

Obviously, those duplicate `SecureStringToCoTaskMemUnicode` should be `SecureStringToGlobalAllocUnicode`

Author: tangentyh

xml/System.Security/SecureString.xml

@@ -129,7 +129,7 @@
   
 -   <xref:System.Runtime.InteropServices.Marshal.SecureStringToCoTaskMemAnsi%2A?displayProperty=nameWithType> and <xref:System.Runtime.InteropServices.Marshal.SecureStringToGlobalAllocAnsi%2A?displayProperty=nameWithType>, which copy the <xref:System.Security.SecureString> string value to an ANSI string in unmanaged memory.  
   
--   <xref:System.Runtime.InteropServices.Marshal.SecureStringToCoTaskMemUnicode%2A?displayProperty=nameWithType> and <xref:System.Runtime.InteropServices.Marshal.SecureStringToCoTaskMemUnicode%2A?displayProperty=nameWithType>, which copy the <xref:System.Security.SecureString> string value to a Unicode string in unmanaged memory.  
+-   <xref:System.Runtime.InteropServices.Marshal.SecureStringToCoTaskMemUnicode%2A?displayProperty=nameWithType> and <xref:System.Runtime.InteropServices.Marshal.SecureStringToGlobalAllocUnicode%2A?displayProperty=nameWithType>, which copy the <xref:System.Security.SecureString> string value to a Unicode string in unmanaged memory.  
   
  Each of these methods creates a clear-text string in unmanaged memory. It is the responsibility of the developer to zero out and free that memory as soon as it is no longer needed. Each of the string conversion and memory allocation methods has a corresponding method to zero out and free the allocated memory:  
   
@@ -139,7 +139,7 @@
 |<xref:System.Runtime.InteropServices.Marshal.SecureStringToCoTaskMemAnsi%2A?displayProperty=nameWithType>|<xref:System.Runtime.InteropServices.Marshal.ZeroFreeCoTaskMemAnsi%2A?displayProperty=nameWithType>|  
 |<xref:System.Runtime.InteropServices.Marshal.SecureStringToCoTaskMemUnicode%2A?displayProperty=nameWithType>|<xref:System.Runtime.InteropServices.Marshal.ZeroFreeCoTaskMemUnicode%2A?displayProperty=nameWithType>|  
 |<xref:System.Runtime.InteropServices.Marshal.SecureStringToGlobalAllocAnsi%2A?displayProperty=nameWithType>|<xref:System.Runtime.InteropServices.Marshal.ZeroFreeGlobalAllocAnsi%2A?displayProperty=nameWithType>|  
-|<xref:System.Runtime.InteropServices.Marshal.SecureStringToCoTaskMemUnicode%2A?displayProperty=nameWithType>|<xref:System.Runtime.InteropServices.Marshal.ZeroFreeGlobalAllocUnicode%2A?displayProperty=nameWithType>|  
+|<xref:System.Runtime.InteropServices.Marshal.SecureStringToGlobalAllocUnicode%2A?displayProperty=nameWithType>|<xref:System.Runtime.InteropServices.Marshal.ZeroFreeGlobalAllocUnicode%2A?displayProperty=nameWithType>|  
   
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