Use venv's python executable

Current ci_build.sh uses the global python executable. If pytest and flake8 are not globally installed `mvn test` will fail. This commit fixes that.

covered by: cerebral-armins-stepanjans.dco

NOTICE.txt

@@ -4,3 +4,5 @@ Licensed under Apache 2.0 license
 
 This product includes software developed at
 The Apache Software Foundation (http://www.apache.org/).
+
+This product contains code copyright Cerebral Adaptive Forecasting, licensed under Apache 2.0 license.

dco/cerebral-armins_stepanjans.dco

@@ -0,0 +1,10 @@
+1) I, Armins Stepanjans, certify that all work committed with the commit message
+"covered by: cerebral-armins_stepanjans.dco" is copyright
+Cerebral Adaptive Forecasting and that I am authorized by Cerebral Adaptive Forecasting
+to contribute this code under the Apache 2.0 license.
+
+2) I understand and agree all contribution including all personal
+information I submit with it is maintained indefinitely and may be
+redistributed consistent with the open source license(s) involved.
+
+This certification is effective for all code contributed from 2023-12-04 to 9999-01-01.

dmn-tck-it/dmn-tck-it-python-translator/ci_build.sh

@@ -18,7 +18,7 @@ fi
 pwd
 ls -la
 
-python -m pytest
+.venv/bin/python -m pytest
 status=$?
 if [ $status -eq 0 ]
 then
@@ -27,7 +27,7 @@ else
   echo "pytest failed"
   exit 1
 fi
-python -m flake8
+.venv/bin/python -m flake8
 status=$?
 if [ $status -eq 0 ]
 then