manifest: replace a realpath with an abspath in ManifestProject

Those aren't the same thing on POSIX, and the Project equivalent is
using abspath. Keep it consistent.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>

src/west/manifest.py

@@ -834,8 +834,8 @@ class ManifestProject(Project):
     @property
     def abspath(self) -> Optional[str]:
         if self._abspath is None and self.topdir and self.path:
-            self._abspath = os.path.realpath(os.path.join(self.topdir,
-                                                          self.path))
+            self._abspath = os.path.abspath(os.path.join(self.topdir,
+                                                         self.path))
         return self._abspath
 
     def as_dict(self) -> Dict: