Restore +x permissions to fbcode_builder/getdeps.py

Summary:
+x permissions were lost in D104495377

citadel-fbcode-post-processing job is failing
https://www.internalfb.com/intern/sandcastle/job/58546795545803121/
```
Script ended with non-zero return code: 126. Stdout: , Stderr: bash: line 1: /data/sandcastle/boxes/trunk-hg-fbcode-fbsource/fbcode/opensource/fbcode_builder/getdeps.py: Permission denied
```

Reviewed By: AyliD

Differential Revision: D104808692

fbshipit-source-id: a3ffc92c6a89bb419d0b8df99b694d95e43531f9

Author: maru