BLD: fix a missing build dependency for cython_special, and add a CI check

This was technically a race condition (no one seems to have hit it yet though).
From the added CI step:

```
Run ninja -C build -t missingdeps
Missing dep: scipy/special/cython_special.cpython-310-x86_64-linux-gnu.so.p/meson-generated_cython_special.c.o uses scipy/special/_ufuncs_defs.h (generated by CUSTOM_COMMAND)
Processed 1310 nodes.
Error: There are 1 missing dependency paths.
1 targets had depfile dependencies on 1 distinct generated inputs (from 1 rules)  without a non-depfile dep path to the generator.
There might be build flakiness if any of the targets listed above are built alone, or not late enough, in a clean output directory.
```

[skip cirrus] [skip circle]

Author: rgommers

.github/workflows/linux.yml

@@ -124,6 +124,9 @@ jobs:
         python dev.py build --tags=runtime,python-runtime,devel,tests
         python tools/check_installation.py ${{ env.INSTALLDIR }}
 
+    - name: Check build-internal dependencies
+      run: ninja -C build -t missingdeps
+
     - name: Mypy
       if: matrix.python-version == '3.10'
       run: |

scipy/special/meson.build

@@ -133,12 +133,12 @@ cython_special_pxd = fs.copyfile('cython_special.pxd')
 uf_cython_gen = generator(cython,
   arguments : cython_args,
   output : '@[email protected]',
-  depends : [_cython_tree, _ufuncs_pxi_pxd_sources, cython_special_pxd])
+  depends : [_cython_tree, _ufuncs_pxi_pxd_sources, cython_special_pxd, cython_special[0]])
 
 uf_cython_gen_cpp = generator(cython,
   arguments : cython_cplus_args,
   output : '@[email protected]',
-  depends : [_cython_tree, _ufuncs_pxi_pxd_sources, cython_special_pxd])
+  depends : [_cython_tree, _ufuncs_pxi_pxd_sources, cython_special_pxd, cython_special[0]])
 
 py3.extension_module('_ufuncs',
   [