Discover Tcl/Tk from Homebrew via pkgconfig for 3.11+ (#2501)

CPython 3.11+ dropped support for --with-tcl-tk-*
in favor of pure pkgconfig

plugins/python-build/test/test_helper.bash

@@ -111,8 +111,10 @@ assert_failure() {
 
 assert_equal() {
   if [ "$1" != "$2" ]; then
-    { echo "expected: $1"
-      echo "actual:   $2"
+    { echo "expected:"
+      echo "$1"
+      echo "actual:"
+      echo "$2"
     } | flunk
   fi
 }