Update Go doc comments to Go 1.19's format

This patch is the result of running Go 1.19's `gofmt` on the codebase,
which automatically updates all Go doc comments to the new format.

https://tip.golang.org/doc/go1.19#go-doc

internal/auth/auth.go

@@ -162,7 +162,8 @@ func (a *Authenticator) Reload() error {
 // DecodeResponse decodes a plain auth response.
 //
 // It must be a a base64-encoded string of the form:
-//   <authorization id> NUL <authentication id> NUL <password>
+//
+//	<authorization id> NUL <authentication id> NUL <password>
 //
 // https://tools.ietf.org/html/rfc4954#section-4.1.
 //