minor refactoring: use path.Dir when splitting a file path into parts in fake_workspace.go (#2621)

## Why
<!-- Why are these changes needed? Provide the context that the reviewer
might be missing.
For example, were there any decisions behind the change that are not
reflected in the code itself? -->
Addresses a comment from #2465

## Tests
<!-- How have you tested the changes? -->
Existing tests

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Author: anton-107

libs/testserver/fake_workspace.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
+	"path"
 	"sort"
 	"strconv"
 	"strings"
@@ -82,23 +83,15 @@ func (s *FakeWorkspace) WorkspaceDelete(path string, recursive bool) {
 	}
 }
 
-func (s *FakeWorkspace) WorkspaceFilesImportFile(path string, body []byte) {
-	if !strings.HasPrefix(path, "/") {
-		path = "/" + path
+func (s *FakeWorkspace) WorkspaceFilesImportFile(filePath string, body []byte) {
+	if !strings.HasPrefix(filePath, "/") {
+		filePath = "/" + filePath
 	}
-	s.files[path] = body
+	s.files[filePath] = body
 
 	// Add all directories in the path to the directories map
-	parts := strings.Split(path, "/")
-	currentPath := ""
-	for i, part := range parts {
-		// Skip empty parts and the last part (which is the file itself)
-		if part == "" || i == len(parts)-1 {
-			continue
-		}
-
-		currentPath = currentPath + "/" + part
-		s.directories[currentPath] = true
+	for dir := path.Dir(filePath); dir != "/"; dir = path.Dir(dir) {
+		s.directories[dir] = true
 	}
 }