Revert x86_64 homebrew location change (with explanation).

.github/workflows/wheels-test.sh

@@ -7,7 +7,10 @@ if [[ "$OSTYPE" == "darwin"* ]]; then
     # However, we *do* need Homebrew to provide a copy of fribidi for
     # testing purposes so that we can verify the fribidi shim works as expected.
     if [[ "$(uname -m)" == "x86_64" ]]; then
-        HOMEBREW_HOME=/usr/local
+        # Use the "installed" location, rather than /usr/local, for two reasons:
+        # firstly, Homebrew allows libraries to be *installed*, but not linked;
+        # and secondly, we don't want any *other* leakage from /usr/local.
+        HOMEBREW_HOME=/usr/local/Homebrew
     else
         HOMEBREW_HOME=/opt/homebrew
     fi