chore: update vendored mimalloc from 2.0.6 to 2.1.7

I can't see a changelog or release notes in the repo, so here is the
diff:

- microsoft/mimalloc@v2.0.6...v2.1.7

Author: wincent

bin/vendor-mimalloc

@@ -12,7 +12,7 @@ BASE=lua/wincent/commandt/lib/vendor/github/microsoft
 mkdir -p "$BASE"
 cd "$BASE"
 rm -rf mimalloc*
-wget https://github.com/microsoft/mimalloc/archive/refs/tags/v2.0.6.tar.gz -O mimalloc.tar.gz
+wget https://github.com/microsoft/mimalloc/archive/refs/tags/v2.1.7.tar.gz -O mimalloc.tar.gz
 tar xzf mimalloc.tar.gz
 rm mimalloc.tar.gz
-ln -s mimalloc-2.0.6 mimalloc
+ln -s mimalloc-2.1.7 mimalloc

lua/wincent/commandt/lib/vendor/github/microsoft/mimalloc

@@ -1 +1 @@
-mimalloc-2.0.6
+mimalloc-2.1.7