Fix nodegit Tree#getEntry return type (#38276)

As per the documentation, Tree#getEntry is an async function and thus
returns a Promise.
See: https://www.nodegit.org/api/tree/#getEntry

types/nodegit/index.d.ts

@@ -3,6 +3,7 @@
 // Definitions by: Dolan Miu <https://github.com/dolanmiu>,
 //                 Tobias Nießen <https://github.com/tniessen>,
 //                 Pierre Vigier <https://github.com/pvigier>
+//                 Jibril Saffi <https://github.com/IGI-111>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
 export { AnnotatedCommit } from './annotated-commit';

types/nodegit/nodegit-tests.ts

@@ -14,6 +14,9 @@ const ref = new Git.Reference();
 const tree = new Git.Tree();
 
 tree.walk().start();
+tree.getEntry("/").then(entry => {
+    // Use entry
+});
 
 // AnnotatedCommit Tests
 

types/nodegit/tree.d.ts

@@ -50,7 +50,7 @@ export class Tree {
     /**
      * Get an entry at a path. Unlike by name, this takes a fully qualified path, like /foo/bar/baz.javascript
      */
-    getEntry(filePath: string): TreeEntry;
+    getEntry(filePath: string): Promise<TreeEntry>;
     /**
      * Return an array of the entries in this tree (excluding its children).
      */