bindings,ci,docs: Raise minimal Python version to 3.8

Python 3.6 and 3.7 are EOL.

doc/tutorial/source/getting-started.rst

@@ -68,7 +68,7 @@ are needed to get started with |ns3|:
 Prerequisite  Package/version
 ============  ===========================================================
 C++ compiler  ``clang++`` or ``g++`` (g++ version 9 or greater)
-Python        ``python3`` version >=3.6
+Python        ``python3`` version >=3.8
 CMake         ``cmake`` version >=3.13
 Build system  ``make``, ``ninja``, ``xcodebuild`` (XCode)
 Git           any recent version (to access |ns3| from `GitLab.com <https://gitlab.com/nsnam/ns-3-dev/>`_)

doc/tutorial/source/quick-start.rst

@@ -33,7 +33,7 @@ does not cover those aspects.
 Prerequisites
 *************
 |ns3| has various optional extensions, but the main features just require
-a C++ compiler (g++ or clang++), Python (version 3.6 or above), CMake and
+a C++ compiler (g++ or clang++), Python (version 3.8 or above), CMake and
 a build-system (e.g. make, ninja, Xcode).
 We focus in this chapter only on getting |ns3| up and running on a system
 supported by a recent C++ compiler and Python runtime support.

setup.cfg

@@ -26,8 +26,6 @@ classifiers =
     Intended Audience :: Developers
     Intended Audience :: Science/Research
     Programming Language :: C++
-    Programming Language :: Python :: 3.6
-    Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
     Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
@@ -38,7 +36,7 @@ classifiers =
 
 [options]
 zip_safe = False
-python_requires = >=3.6
+python_requires = >=3.8
 install_requires =
     cppyy==3.1.2
 

utils/tests/gitlab-ci-code-linting.yml

@@ -152,6 +152,6 @@ python-format-latest:
   extends: .python-format
   image: python:latest
 
-python-format-3.6:
+python-format-3.8:
   extends: .python-format
-  image: python:3.6
+  image: python:3.8