Fix build script due to failing deploy

Context: python3.8-venv on Netlify build image doesn't
preinstalled, so we need to hack around on feature flags.

Signed-off-by: Andrei Jiroh Halili <ajhalili2006@andreijiroh.eu.org>

scripts/build.sh

 #!/bin/bash
 
-python3 -m venv .venv
-source .venv/bin/activate
+if [[ $FF_DISABLE_VENV_USAGE_DURING_BUILD != "false" ]]; then
+  python3 -m venv .venv
+  source .venv/bin/activate
+fi
 
 pip3 install -r requirements.txt --upgrade