build: pin direct test dependencies

Fixes #1899
Reverts #1867

In #1867 we started pinning direct and transitive test
dependencies for stable test results, i.e. to not have an unnoticed
update of a used test tool (or their dependencies) break our tests.

This resulted in a dependabot updates inundating our PR tracker,
potentially obfuscating updates, which we care to address with
higher priority.

As a compromise we now only pin direct test dependencies, which
should still give us relatively stable test runs, while reducing
the spam.

Signed-off-by: Lukas Puehringer <lukas.puehringer@nyu.edu>

Author: Lukas Puehringer

requirements-test.txt

@@ -4,10 +4,10 @@
 -r requirements-pinned.txt
 
 # additional test tools for linting and coverage measurement
-coverage
-black
-isort
-pylint
-mypy
-bandit
-types-requests
+coverage==6.3.2
+black==22.1.0
+isort==5.10.1
+pylint==2.12.2
+mypy==0.941
+bandit==1.7.4
+types-requests==2.27.14