Fix GitHub Actions Cache setting an incorrect Content-Range header

Content-Range is 0 indexed, although nobody seemed to have encountered
any issues as a result of this on github.com, but on GitHub Enterprise
server it resulted in a InvalidChunkException error

src/vcpkg/binarycaching.cpp

@@ -930,7 +930,7 @@ namespace
                     m_token_header,
                     m_accept_header.to_string(),
                     "Content-Type: application/octet-stream",
-                    "Content-Range: bytes 0-" + std::to_string(cache_size) + "/*",
+                    "Content-Range: bytes 0-" + std::to_string(cache_size - 1) + "/*",
                 };
 
                 PrintingDiagnosticContext pdc{msg_sink};