Put smoke test deps in requirements.txt for Dependabot (#7806)

testing/plugins_integration/requirements.txt

@@ -0,0 +1,15 @@
+anyio[curio,trio]==2.0.0
+django==3.1.1
+pytest-asyncio==0.14.0
+pytest-bdd==4.0.1
+pytest-cov==2.10.1
+pytest-django==3.10.0
+pytest-flakes==4.0.2
+pytest-html==2.1.1
+pytest-mock==3.3.1
+pytest-rerunfailures==9.1.1
+pytest-sugar==0.9.4
+pytest-trio==0.6.0
+pytest-twisted==1.13.2
+twisted==20.3.0
+pytest-xvfb==2.0.0