Add .pytest_cache to .gitignore (GH-16595)

diff --git a/.gitignore b/.gitignore
index 0e3f973..b11f72f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -33,6 +33,7 @@
 gmon.out
 .coverage
 .mypy_cache/
+.pytest_cache/
 
 *.exe
 !Lib/distutils/command/*.exe