Migrate to go-git/go-git v5.0.0 (#10735)

vendor/github.com/go-git/go-billy/v5/README.md

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+# go-billy [![GoDoc](https://godoc.org/gopkg.in/go-git/go-billy.v5?status.svg)](https://pkg.go.dev/github.com/go-git/go-billy) [![Test](https://github.com/go-git/go-billy/workflows/Test/badge.svg)](https://github.com/go-git/go-billy/actions?query=workflow%3ATest)
+
+The missing interface filesystem abstraction for Go.
+Billy implements an interface based on the `os` standard library, allowing to develop applications without dependency on the underlying storage. Makes it virtually free to implement mocks and testing over filesystem operations.
+
+Billy was born as part of [go-git/go-git](https://github.com/go-git/go-git) project.
+
+## Installation
+
+```go
+import "github.com/go-git/go-billy/v5" // with go modules enabled (GO111MODULE=on or outside GOPATH)
+import "github.com/go-git/go-billy" // with go modules disabled
+```
+
+## Usage
+
+Billy exposes filesystems using the
+[`Filesystem` interface](https://pkg.go.dev/github.com/go-git/go-billy/v5?tab=doc#Filesystem).
+Each filesystem implementation gives you a `New` method, whose arguments depend on
+the implementation itself, that returns a new `Filesystem`.
+
+The following example caches in memory all readable files in a directory from any
+billy's filesystem implementation.
+
+```go
+func LoadToMemory(origin billy.Filesystem, path string) (*memory.Memory, error) {
+	memory := memory.New()
+
+	files, err := origin.ReadDir("/")
+	if err != nil {
+		return nil, err
+	}
+
+	for _, file := range files {
+		if file.IsDir() {
+			continue
+		}
+
+		src, err := origin.Open(file.Name())
+		if err != nil {
+			return nil, err
+		}
+
+		dst, err := memory.Create(file.Name())
+		if err != nil {
+			return nil, err
+		}
+
+		if _, err = io.Copy(dst, src); err != nil {
+			return nil, err
+		}
+
+		if err := dst.Close(); err != nil {
+			return nil, err
+		}
+
+		if err := src.Close(); err != nil {
+			return nil, err
+		}
+	}
+
+	return memory, nil
+}
+```
+
+## Why billy?
+
+The library billy deals with storage systems and Billy is the name of a well-known, IKEA
+bookcase. That's it.
+
+## License
+
+Apache License Version 2.0, see [LICENSE](LICENSE)