Update requirements for tests

This commit is intended to be purely an update of the frozen
requirements. However we'd get new warnings with the new version of
pylint. For that reason, the pylint requirement has now been pinned to
what we had in the frozen requirements before.

Each time we want to upgrade pylint, we will need to change this
manually.

---

Among other things, I have noticed that older versions of grpcio take it
much longer (comparatively) to be installed on Python 3.9 compared to
the newer versions.
diff --git a/requirements/cov-requirements.txt b/requirements/cov-requirements.txt
index 3296a3f..e0e8c3b 100644
--- a/requirements/cov-requirements.txt
+++ b/requirements/cov-requirements.txt
@@ -1,16 +1,15 @@
 coverage==4.4
-pytest-cov==2.10.0
-pytest==6.0.1
+pytest-cov==2.10.1
+pytest==6.1.2
 Cython==0.29.21
 ## The following requirements were added by pip freeze:
-attrs==19.3.0
-importlib-metadata==1.7.0
-iniconfig==1.0.1
-more-itertools==8.4.0
+attrs==20.2.0
+importlib-metadata==2.0.0
+iniconfig==1.1.1
 packaging==20.4
 pluggy==0.13.1
 py==1.9.0
 pyparsing==2.4.7
 six==1.15.0
-toml==0.10.1
-zipp==3.1.0
+toml==0.10.2
+zipp==3.4.0
diff --git a/requirements/dev-requirements.in b/requirements/dev-requirements.in
index 5809351..1b3c518 100644
--- a/requirements/dev-requirements.in
+++ b/requirements/dev-requirements.in
@@ -1,5 +1,5 @@
 pexpect
-pylint
+pylint == 2.5.3
 # Pytest 6.0.0 doesn't play well with pylint
 pytest >= 6.0.1
 pytest-datafiles >= 2.0
diff --git a/requirements/dev-requirements.txt b/requirements/dev-requirements.txt
index b6b9e83..fe09d45 100644
--- a/requirements/dev-requirements.txt
+++ b/requirements/dev-requirements.txt
@@ -1,23 +1,22 @@
 pexpect==4.8.0
 pylint==2.5.3
 # Pytest 6.0.0 doesn't play well with pylint
-pytest==6.0.1
+pytest==6.1.2
 pytest-datafiles==2.0
 pytest-env==0.6.2
-pytest-xdist==1.34.0
+pytest-xdist==2.1.0
 pytest-timeout==1.4.2
 pyftpdlib==1.5.6
 ## The following requirements were added by pip freeze:
 apipkg==1.5
 astroid==2.4.2
-attrs==19.3.0
+attrs==20.2.0
 execnet==1.7.1
-importlib-metadata==1.7.0
-iniconfig==1.0.1
+importlib-metadata==2.0.0
+iniconfig==1.1.1
 isort==4.3.21
 lazy-object-proxy==1.4.3
 mccabe==0.6.1
-more-itertools==8.4.0
 packaging==20.4
 pluggy==0.13.1
 ptyprocess==0.6.0
@@ -25,7 +24,7 @@
 pyparsing==2.4.7
 pytest-forked==1.3.0
 six==1.15.0
-toml==0.10.1
+toml==0.10.2
 typed-ast==1.4.1
 wrapt==1.12.1
-zipp==3.1.0
+zipp==3.4.0
diff --git a/requirements/requirements.txt b/requirements/requirements.txt
index 57063c0..6c70265 100644
--- a/requirements/requirements.txt
+++ b/requirements/requirements.txt
@@ -1,13 +1,13 @@
-grpcio==1.30.0
+grpcio==1.33.2
 Jinja2==2.11.2
 pluginbase==1.0.0
-protobuf==3.12.4
-psutil==5.7.2
-ruamel.yaml==0.16.10
-ruamel.yaml.clib==0.2.0
-setuptools==41.6.0
+protobuf==3.13.0
+psutil==5.7.3
+ruamel.yaml==0.16.12
+ruamel.yaml.clib==0.2.2
+setuptools==40.8.0
 pyroaring==0.2.9
-ujson==3.1.0
+ujson==4.0.1
 python-dateutil==2.8.1
 ## The following requirements were added by pip freeze:
 click==7.1.2