python3Packages.pytest-forked: simplify setup hook

We need to make sure that pytest-forked's setup hook runs before the
pytestCheckPhase. Instead of mangling the preDistPhases in a complex
way, we can just set our environment variables in postInstallCheckHook,
which is run right before all preDistPhases.

pkgs/development/python-modules/pytest-forked/setup-hook.sh

@@ -12,21 +12,7 @@ pytestForkedHook() {
     fi
 }
 
-# the flags should be added before pytestCheckHook runs so
-# until we have dependency mechanism in generic builder, we need to use this ugly hack.
-
 if [ -z "${dontUsePytestForked-}" ] && [ -z "${dontUsePytestCheck-}" ]; then
-    if [[ " ${preDistPhases[*]:-} " =~ " pytestCheckPhase " ]]; then
-        _preDistPhases="${preDistPhases[*]} "
-        _preDistPhases="${_preDistPhases/ pytestCheckPhase / pytestForkedHook pytestCheckPhase }"
-        if [[ -n "${__structuredAttrs-}" ]]; then
-            preDistPhases=()
-        else
-            preDistPhases=""
-        fi
-        appendToVar preDistPhases $_preDistPhases
-        unset _preDistPhases
-    else
-        appendToVar preDistPhases pytestForkedHook
-    fi
+    # The flags should be added before pytestCheckHook runs in preDistPhases.
+    postInstallCheckHooks+=(pytestForkedHook)
 fi