Fix tox

tox4 errors if basepython and python in other envs are different. [1]

Bumped tox minversion as allowlist_externals is only supported in 3.18
[2]

[1] https://github.com/tox-dev/tox/issues/2838
[2] https://github.com/tox-dev/tox/issues/2730

Change-Id: I9d24395a7cc5d8423a58ec1e3ed8468ca6984e77

tox.ini

@@ -1,7 +1,8 @@
 [tox]
 envlist = pep8,eslint,karma-local,docs-local,releasenotes
-minversion = 2.3.2
+minversion = 3.18
 skipsdist = True
+ignore_basepython_conflict=true
 
 [testenv]
 basepython = python3
@@ -55,7 +56,7 @@ commands =
   {[testenv]commands}
 
 [testenv:eslint]
-whitelist_externals =
+allowlist_externals =
   npm
 commands =
   npm install
@@ -65,15 +66,15 @@ commands =
 # from master branch into karma environment with python3.x for testing javascripts.
 # Horizon from master is needed to be cloned into ../horizon on both local and CI.
 [testenv:karma]
-whitelist_externals =
-  {[testenv:eslint]whitelist_externals}
+allowlist_externals =
+  {[testenv:eslint]allowlist_externals}
 commands =
   npm install
   npm run test
 
 [testenv:karma-local]
-whitelist_externals =
-  {[testenv:eslint]whitelist_externals}
+allowlist_externals =
+  {[testenv:eslint]allowlist_externals}
 commands =
   {[testenv:karma]commands}
 
@@ -89,7 +90,7 @@ commands=
 
 [testenv:pdf-docs]
 deps = {[testenv:docs]deps}
-whitelist_externals =
+allowlist_externals =
   make
   rm
 commands =
@@ -109,3 +110,5 @@ deps =
   {[testenv:docs]deps}
 commands =
   sphinx-build -a -E -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
+
+# dummy