gh-37522: Add `mypy.ini`
    
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Configuration from
#36198 (comment)
@fchapoton @jhpalmieri


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URL: #37522
Reported by: Matthias Köppe
Reviewer(s): Frédéric Chapoton

Author: Release Manager

src/mypy.ini

@@ -0,0 +1,7 @@
+# https://mypy.readthedocs.io/en/stable/config_file.html
+[mypy]
+python_version = 3.9
+
+# https://github.com/sagemath/sage/issues/36198#issuecomment-1709521850
+follow_imports = skip
+ignore_missing_imports = True