macdeploy: use plugins dir to find plugins

Rather than looking for /translations, which might not exist (it doesn't
in a recent brew installed qt on macOS). i.e:
```bash
ls /opt/homebrew/opt/qtbase/share/qt
doc
libexec
metatypes
mkspecs
modules
plugins
sbom
```

contrib/macdeploy/macdeployqtplus

@@ -160,7 +160,7 @@ class DeploymentInfo(object):
 
     def detectQtPath(self, frameworkDirectory: str):
         parentDir = os.path.dirname(frameworkDirectory)
-        if os.path.exists(os.path.join(parentDir, "share", "qt", "translations")):
+        if os.path.exists(os.path.join(parentDir, "share", "qt", "plugins")):
             self.qtPath = parentDir
         else:
             self.qtPath = os.getenv("QTDIR", None)