Proactively bump golang.org/x/net to v0.12.0

Proactively bump to v0.12.0 to avoid v0.10.0 and v0.11.0, which contain
a regression added by commit
82780d606d.
This commit was later reverted in v0.12.0.

Generated with:

hack/pin-dependency.sh golang.org/x/net v0.12.0 && hack/update-vendor.sh

vendor/golang.org/x/term/term_unix.go

@@ -60,7 +60,7 @@ func restore(fd int, state *State) error {
 func getSize(fd int) (width, height int, err error) {
 	ws, err := unix.IoctlGetWinsize(fd, unix.TIOCGWINSZ)
 	if err != nil {
-		return -1, -1, err
+		return 0, 0, err
 	}
 	return int(ws.Col), int(ws.Row), nil
 }