Update to the latest version of jinja2 (#6790)

lib/spack/external/jinja2/AUTHORS

lib/spack/external/jinja2/LICENSE

lib/spack/external/jinja2/README.rst

lib/spack/external/jinja2/__init__.py

lib/spack/external/jinja2/_identifier.py

lib/spack/external/jinja2/_stringdefs.py

lib/spack/external/jinja2/asyncsupport.py

lib/spack/external/jinja2/bccache.py

lib/spack/external/jinja2/compiler.py

lib/spack/external/jinja2/debug.py

lib/spack/external/jinja2/defaults.py

lib/spack/external/jinja2/environment.py

lib/spack/external/jinja2/ext.py

lib/spack/external/jinja2/filters.py

lib/spack/external/jinja2/idtracking.py

lib/spack/external/jinja2/lexer.py

lib/spack/external/jinja2/nativetypes.py

lib/spack/external/jinja2/nodes.py

lib/spack/external/jinja2/parser.py

lib/spack/external/jinja2/runtime.py