crypto: windows: use LPCTSTR for the temp registry buffer

crypto: windows: use LPCTSTR for the temp registry buffer

mingw-w64 only defines LPCTCH when UNICODE isn't defined
crypto/defaults.c: In function 'get_windows_regdirs':
crypto/defaults.c:72:5: error: unknown type name 'LPCTCH'; did you mean 'LPTCH'?
   72 |     LPCTCH tempstr = NULL;
      |     ^~~~~~
      |     LPTCH

Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/26566)