Update respx to 0.21.0 (#114163)

requirements_test.txt

@@ -31,7 +31,7 @@ pytest-picked==0.5.0
 pytest-xdist==3.3.1
 pytest==8.1.1
 requests-mock==1.11.0
-respx==0.20.2
+respx==0.21.0
 syrupy==4.6.1
 tqdm==4.66.2
 types-aiofiles==23.2.0.20240106