fix broken type annotation imports being ignored

If an annotation could not be resolved, it's classified as a "missing
import" and our configuration ignored it:

```
Skipping analyzing "mesonbuild.backends": module is installed, but missing library stubs or py.typed marker
```

As far as mypy is concerned, this library may or may not exist, but it
doesn't have any typing information at all (may need to be installed
first).

We ignored this because of our docs/ and tools/ thirdparty dependencies,
but we really should not. It is trivial to install them, and then
enforce that this "just works".

By enforcing it, we also make sure typos get caught.

1 files changed, 1 insertions, 1 deletions

diff --git a/.mypy.ini b/.mypy.ini
index 70fdcd9..d00944b 100644
--- a/.mypy.ini
+++ b/.mypy.ini
@@ -2,7 +2,7 @@
 strict_optional               = False
 show_error_context            = False
 show_column_numbers           = True
-ignore_missing_imports        = True
+ignore_missing_imports        = False
 implicit_reexport             = False
 
 follow_imports                = silent