chore: modernize CI and update Go toolchain

- Bump Go from 1.19 to 1.26 and update all dependencies
- Rewrite CI workflow with matrix strategy (Linux, macOS, Windows)
- Update GitHub Actions to current versions (checkout@v4, setup-go@v5)
- Update CodeQL actions from v1 to v3
- Fix cross-platform bug in mock/path.go (path.Join -> filepath.Join)
- Clean up dependabot config (weekly schedule, remove stale ignore)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

vendor/github.com/Microsoft/go-winio/internal/socket/socket.go

@@ -156,9 +156,7 @@ func connectEx(
 	bytesSent *uint32,
 	overlapped *windows.Overlapped,
 ) (err error) {
-	// todo: after upgrading to 1.18, switch from syscall.Syscall9 to syscall.SyscallN
-	r1, _, e1 := syscall.Syscall9(connectExFunc.addr,
-		7,
+	r1, _, e1 := syscall.SyscallN(connectExFunc.addr,
 		uintptr(s),
 		uintptr(name),
 		uintptr(namelen),
@@ -166,8 +164,8 @@ func connectEx(
 		uintptr(sendDataLen),
 		uintptr(unsafe.Pointer(bytesSent)),
 		uintptr(unsafe.Pointer(overlapped)),
-		0,
-		0)
+	)
+
 	if r1 == 0 {
 		if e1 != 0 {
 			err = error(e1)