Download, verify, build, and cache Python3

.gitlab-ci.yml

 test-job1:
   stage: test
+  variables:
+    PY_VERSION: "3.11.8"
   script:
     - python3 --version
+    - mkdir binaries
+    - pushd binaries
+    - touch ./py_keyring
+    - wget -O - https://github.com/Yhg1s.gpg | gpg --import --keyring ./py_keyring
+    - wget -O - https://keybase.io/pablogsal/pgp_keys.asc?fingerprint=a035c8c19219ba821ecea86b64e628f8d684696d | gpg --import --keyring ./py_keyring
+    - wget -O - https://keybase.io/ambv/pgp_keys.asc?fingerprint=e3ff2839c048b25c084debe9b26995e310250568 | gpg --import --keyring ./py_keyring
+    - wget https://www.python.org/ftp/python/${PY_VERSION}/Python-${PY_VERSION}.tar.xz.asc
+    - wget https://www.python.org/ftp/python/${PY_VERSION}/Python-${PY_VERSION}.tar.xz
+    - gpg --verify --keyring ./py_keyring ./Python-${PY_VERSION}.tar.xz.asc
+    - tar xvf ./Python-${PY_VERSION}.tar.xz
+    - pushd Python-${PY_VERSION}
+    - PY_DIR=$(readlink -f .)
+    - ./configure --prefix ${PY_DIR} --enable-optimizations
+    - make
+    - make test
+    - make altinstall
+    - popd
+    - popd
+    - ${PY_DIR}/bin/python --version
+  cache:
+    key: binaries-cache-$CI_COMMIT_REF_SLUG
+    paths:
+      - binaries/