gh-128696: Add arm64 to the get_platform return val description (#128701)

Author: rruuaanng

Doc/library/sysconfig.rst

@@ -388,7 +388,8 @@ Other functions
 
    Windows will return one of:
 
-   - win-amd64 (64bit Windows on AMD64, aka x86_64, Intel64, and EM64T)
+   - win-amd64 (64-bit Windows on AMD64, aka x86_64, Intel64, and EM64T)
+   - win-arm64 (64-bit Windows on ARM64, aka AArch64)
    - win32 (all others - specifically, sys.platform is returned)
 
    macOS can return:

Lib/sysconfig/__init__.py

@@ -616,7 +616,8 @@ def get_platform():
        solaris-2.6-sun4u
 
     Windows will return one of:
-       win-amd64 (64bit Windows on AMD64 (aka x86_64, Intel64, EM64T, etc)
+       win-amd64 (64-bit Windows on AMD64 (aka x86_64, Intel64, EM64T, etc)
+       win-arm64 (64-bit Windows on ARM64 (aka AArch64)
        win32 (all others - specifically, sys.platform is returned)
 
     For other non-POSIX platforms, currently just returns 'sys.platform'.