Dependencies: add upper limit for pytest-asyncio (#5309)

The just released version v0.17 of `pytest-asyncio` causes the async
tests in `tests/engine/test_utils.py` to fail. For now we are putting an
upper limit on the requirement until a proper solution is found.

Cherry-pick: afebb6e

setup.json

@@ -108,8 +108,8 @@
             "aiida-export-migration-tests==0.9.0",
             "pg8000~=1.13",
             "pgtest~=1.3,>=1.3.1",
-            "pytest~=6.0",
-            "pytest-asyncio~=0.12",
+            "pytest~=6.2",
+            "pytest-asyncio~=0.12,<0.17",
             "pytest-timeout~=1.3",
             "pytest-cov~=2.7,<2.11",
             "pytest-rerunfailures~=9.1,>=9.1.1",