Brewfile: don't install osxfuse cask by default.

Brewfile

@@ -3,4 +3,10 @@ brew 'zstd'
 brew 'lz4'
 brew 'xxhash'
 brew 'openssl@1.1'
-cask 'osxfuse'  # Required for Python llfuse module
+
+# osxfuse (aka macFUSE) is only required for "borg mount",
+# but won't work on github actions' workers.
+# it requires installing a kernel extension, so some users
+# may want it and some won't.
+
+#cask 'osxfuse'