tests/extmod/vfs_fat_finaliser.py: Tweak test so files are collected.

Signed-off-by: Damien George <damien@micropython.org>

tests/extmod/vfs_fat_finaliser.py

@@ -64,7 +64,7 @@ import gc
 # in turn allocate new qstrs and/or a new qstr pool).
 f = None
 n = None
-names = ["x%d" % i for i in range(4)]
+names = ["x%d" % i for i in range(5)]
 
 # Do a large number of single-block allocations to move the GC head forwards,
 # ensuring that the files are allocated from never-before-used blocks and
@@ -74,12 +74,13 @@ for i in range(1024):
     []
 
 # Run the test: create files without closing them, run GC, then read back files.
+# Only read back N-1 files because the last one may not be finalised due to
+# references to it being left on the C stack.
 for n in names:
     f = vfs.open(n, "w")
     f.write(n)
     f = None  # release f without closing
-    sorted([0, 1, 2, 3], key=lambda x: x)  # use up Python and C stack so f is really gone
-gc.collect()  # should finalise all N files by closing them
-for n in names:
+gc.collect()  # should finalise at least the first N-1 files by closing them
+for n in names[:-1]:
     with vfs.open(n, "r") as f:
         print(f.read())