Add vendor

Specifically because I want to modify a dependency

vendor/github.com/muesli/cancelreader/cancelreader_default.go

@@ -0,0 +1,12 @@
+//go:build !darwin && !windows && !linux && !solaris && !freebsd && !netbsd && !openbsd && !dragonfly
+// +build !darwin,!windows,!linux,!solaris,!freebsd,!netbsd,!openbsd,!dragonfly
+
+package cancelreader
+
+import "io"
+
+// NewReader returns a fallbackCancelReader that satisfies the CancelReader but
+// does not actually support cancellation.
+func NewReader(reader io.Reader) (CancelReader, error) {
+	return newFallbackCancelReader(reader)
+}