fontmake installation error with python 3.10

After upgrading to python 3.10, I made a new virtualenv and then tried installing fontmake using `pip install fontmake`

I get the following error:
```
…
In file included from src/lxml/etree.c:810:
src/lxml/includes/etree_defs.h:14:10: fatal error: 'libxml/xmlversion.h' file not found
#include "libxml/xmlversion.h"
^~~~~~~~~~~~~~~~~~~~~
1 error generated.
Compile failed: command '/usr/bin/clang' failed with exit code 1
cc -I/usr/include/libxml2 -c /var/folders/6b/yq0dskg15kqdkn3_k2457hk00000gn/T/xmlXPathInitn415fkns.c -o var/folders/6b/yq0dskg15kqdkn3_k2457hk00000gn/T/xmlXPathInitn415fkns.o
/var/folders/6b/yq0dskg15kqdkn3_k2457hk00000gn/T/xmlXPathInitn415fkns.c:1:10: fatal error: 'libxml/xpath.h' file not found
#include "libxml/xpath.h"
^~~~~~~~~~~~~~~~
1 error generated.
*********************************************************************************
Could not find function xmlCheckVersion in library libxml2. Is libxml2 installed?
Perhaps try: xcode-select --install
*********************************************************************************
error: command '/usr/bin/clang' failed with exit code 1
[end of output]

note: This error originates from a subprocess, and is likely not a problem with pip.
error: legacy-install-failure

× Encountered error while trying to install package.
╰─> lxml

note: This is an issue with the package mentioned above, not pip.
hint: See above for output from the failure.
```

Then I tried making another virtualenv specifying the older python version 3.9, and then when I run `pip install fontmake` I don't get any tracebacks. I found this while helping someone install fontmake on a new computer and they had the issue too with the newer python version.

Are there different installation instructions for python 3.10 or newer? Thanks!