Fix: downgrade numpy version to 1.21.3

Recent ethos-u-vela version 3.5.0 does not support numpy version higher
than 1.21.3. Downgrading numpy version to 1.21.3 for
set_up_default_resources.py script to install proper packages.

Change-Id: I15d8b1dbe04e974ebb140f99ba0f17bf6ee4f933
Signed-off-by: Maksims Svecovs <maksims.svecovs@arm.com>
diff --git a/scripts/py/requirements.txt b/scripts/py/requirements.txt
index 966dc82..3057913 100644
--- a/scripts/py/requirements.txt
+++ b/scripts/py/requirements.txt
@@ -3,7 +3,7 @@
 llvmlite==0.38.0
 MarkupSafe==1.1.1
 numba==0.55.1
-numpy==1.21.6
+numpy==1.21.3
 Pillow==7.2.0
 pycparser==2.20
 resampy==0.2.2