Replace deprecated setup.py install method with direct pip equivalent

Fixes `SetuptoolsDeprecationWarning` warnings during Pyscan installation.
See:
- https://blog.ganssle.io/articles/2021/10/setup-py-deprecated.html
- pypa/setuptools#917

infra/base-images/base-builder/compile_python_fuzzer

@@ -32,7 +32,7 @@ if [[ $SANITIZER = *introspector* ]]; then
  # we enter the virtual environment in the following lines because we need
  # to use the same python environment that installed the fuzzer dependencies.
  python3 /fuzz-introspector/frontends/python/prepare_fuzz_imports.py $fuzzer_path isossfuzz
- 
+
  # We must ensure python3.9, this is because we use certain
  # AST logic from there.
  # The below should probably be refined
@@ -84,7 +84,7 @@ then
  if [[ ! -d "/pysecsan" ]];
  then
  pushd /usr/local/lib/sanitizers/pysecsan
- python3 setup.py install
+ python3 -m pip install .
  popd
  fi