Re-add python install of requirements to Travis CI.

Also correct 'distro to 'dist' and update ubuntu to jammy and python
to 3.10 to attempt to fend off future issues. Too much got removed
when disabling travis and the Coverity scan build was failing on 'make
generated-files', due to lack of installed python dependencies.

Signed-off-by: Paul Elliott <paul.elliott@arm.com>

.travis.yml

@@ -1,9 +1,9 @@
 # Declare python as our language. This way we get our chosen Python version,
 # and pip is available. Gcc and clang are available anyway.
-distro: xenial
+dist: jammy
 os: linux
 language: python
-python: 3.5
+python: 3.10
 
 cache: ccache
 
@@ -11,6 +11,9 @@ branches:
   only:
     coverity_scan
 
+install:
+  - $PYTHON scripts/min_requirements.py
+
 env:
   global:
     - SEED=1