[FIX] runbot: pin matplotlib 1.22

See 66a1018#r144596695

Looks like 1.21.5 is not available on some distribution

1.22 should be available on most system.

Note that the prefered solution would be to install matplotlib using
apt install python3-matplotlib as stated in the readme.

requirements.txt

@@ -1,5 +1,5 @@
 matplotlib==3.5.1
-numpy==1.21.5 # for matplotlib compatibility
+numpy==1.22.0 # for matplotlib compatibility, 1.21.5 on jammy, but this version is not available on some distributions because of CVE
 unidiff
 docker==4.1.0; python_version < '3.10'
 docker==5.0.3; python_version >= '3.10'  # (Jammy)