tools/pygrub: Fix bug in LIMIT_FSIZE env variable override

The env variable must be interpreted as an integer. As it is, the override
logic simply causes an exception.

Fixes: e0342ae555 ("tools/pygrub: Deprivilege pygrub")
Signed-off-by: Alejandro Vallejo <alejandro.vallejo@cloud.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

tools/pygrub/src/pygrub

@@ -89,7 +89,7 @@ def downgrade_rlimits():
     # write permissions are bound.
     fsize = LIMIT_FSIZE
     if "PYGRUB_MAX_FILE_SIZE_MB" in os.environ.keys():
-        fsize = os.environ["PYGRUB_MAX_FILE_SIZE_MB"] << 20
+        fsize = int(os.environ["PYGRUB_MAX_FILE_SIZE_MB"]) << 20
 
     resource.setrlimit(resource.RLIMIT_FSIZE, (fsize, fsize))