CDRIVER-5913 Fix Windows compilation under C23

[jeroen]

Fixes an error with gcc in c23 mode:

gcc  -DNDEBUG -I. -Icommon -Ikms -Iutf8proc -DBSON_COMPILATION -DMONGOC_COMPILATION -DMONGOC_ENABLE_SSL_SECURE_CHANNEL -DMONGOC_ENABLE_CRYPTO_CNG -DKMS_MESSAGE_ENABLE_CRYPTO -DKMS_MESSAGE_ENABLE_CRYPTO_CNG -DMONGOC_HAVE_SASL_CLIENT_DONE -D__USE_MINGW_ANSI_STDIO -DKMS_MESSAGE_LITTLE_ENDIAN -DUTF8PROC_STATIC -DMONGOC_HAVE_BCRYPT_PBKDF2    -I"C:/rtools44/x86_64-w64-mingw32.static.posix/include"      -O2 -Wall -std=gnu2x  -mfpmath=sse -msse2 -mstackrealign   -c mongoc/mongoc-secure-channel.c -o mongoc/mongoc-secure-channel.o
mongoc/mongoc-secure-channel.c: In function 'mongoc_secure_channel_setup_certificate_from_file':
mongoc/mongoc-secure-channel.c:67:14: error: incompatible types when returning type '_Bool' but 'PCCERT_CONTEXT' {aka 'const CERT_CONTEXT *'} was expected
   67 |       return false;
      |              ^~~~~
mongoc/mongoc-secure-channel.c:75:14: error: incompatible types when returning type '_Bool' but 'PCCERT_CONTEXT' {aka 'const CERT_CONTEXT *'} was expected
   75 |       return false;
      |              ^~~~~
make: *** [C:/R/etc/x64/Makeconf:289: mongoc/mongoc-secure-channel.o] Error 1

[kevinAlbs]

Thank you for the fix @jeroen. LGTM.

Related: CI testing for C23 is in progress (CDRIVER-5891).