build: modernize Go code with go fix for go1.25

backend/shade/shade.go

@@ -163,7 +163,7 @@ func (f *Fs) refreshJWTToken(ctx context.Context) (string, error) {
 	if err != nil {
 		return "", fmt.Errorf("invalid token received from server")
 	}
-	var claims map[string]interface{}
+	var claims map[string]any
 	if err := json.Unmarshal(payload, &claims); err != nil {
 		return "", err
 	}
@@ -182,7 +182,7 @@ func (f *Fs) refreshJWTToken(ctx context.Context) (string, error) {
 	return f.token, nil
 }
 
-func (f *Fs) callAPI(ctx context.Context, method, path string, response interface{}) (*http.Response, error) {
+func (f *Fs) callAPI(ctx context.Context, method, path string, response any) (*http.Response, error) {
 	token, err := f.refreshJWTToken(ctx)
 	if err != nil {
 		return nil, err

backend/shade/upload.go

@@ -7,6 +7,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"maps"
 	"net/http"
 	"net/url"
 	"path"
@@ -203,9 +204,7 @@ func (s *shadeChunkWriter) WriteChunk(ctx context.Context, chunkNumber int, read
 	var uploadRes *http.Response
 	if len(partURL.Headers) > 0 {
 		opts.ExtraHeaders = make(map[string]string)
-		for k, v := range partURL.Headers {
-			opts.ExtraHeaders[k] = v
-		}
+		maps.Copy(opts.ExtraHeaders, partURL.Headers)
 	}
 
 	err = s.f.pacer.Call(func() (bool, error) {