unittests: migrate from jsonschema to fastjsonschema

The former has rust dependencies, which lead to max capping on Cygwin
since there is no rust compiler there. But it turns out there are other
disadvantages of jsonschema:

- it involves installing 5 wheels, instead of just 1
- it is much slower

To give some perspective to the latter issue, this is what it looks like
when I test with jsonschema:

```
===== 1 passed, 509 deselected in 3.07s =====
Total time: 3.341 seconds
```

And here's what it looks like when I test with fastjsonschema:
```
===== 1 passed, 509 deselected, 1 warning in 0.28s =====
Total time: 0.550 seconds
```

I cannot think of a good reason to use the former. Although in order to
work on old CI images, we'll support it as a fallback mechanism

1 files changed, 1 insertions, 1 deletions

diff --git a/.github/workflows/macos.yml b/.github/workflows/macos.yml
index 6d6b43af7..0e5002a40 100644
--- a/.github/workflows/macos.yml
+++ b/.github/workflows/macos.yml
@@ -33,7 +33,7 @@ jobs:
         python-version: '3.x'
     - run: |
         python -m pip install --upgrade pip
-        python -m pip install pytest pytest-xdist pytest-subtests jsonschema coverage
+        python -m pip install pytest pytest-xdist pytest-subtests fastjsonschema coverage
     - run: brew install pkg-config ninja llvm qt@5
     - env:
         CPPFLAGS: "-I/usr/local/include"