[travis] installation fixes

.travis.yml

@@ -1,4 +1,4 @@
-dist: focal
+dist: jammy
 language: python
 sudo: required
 cache:
@@ -26,7 +26,8 @@ python:
   - '3.7'
 
 install:
-  - pip install --ignore-installed six # install six inside the venv since the system version is too old
+  - mkdir -p ~/.cache/pip/wheels # remove warning "Url 'file:///home/travis/.cache/pip/wheels' is ignored: it is neither a file nor a directory."
+  - pip install --ignore-installed setuptools pip six certifi # install packages inside the venv if the system version is too old
   - pip install numpy
   - pip install GDAL==$(gdal-config --version) --global-option=build_ext --global-option="$(gdal-config --cflags)"
   - pip install -r requirements.txt