restore: use case insensitive file name comparison on windows

internal/restorer/restorer_unix.go

@@ -0,0 +1,10 @@
+//go:build !windows
+// +build !windows
+
+package restorer
+
+// toComparableFilename returns a filename suitable for equality checks. On Windows, it returns the
+// uppercase version of the string. On all other systems, it returns the unmodified filename.
+func toComparableFilename(path string) string {
+	return path
+}