Use the standard PIP_CACHE_DIR for Python dependency caching template

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

changelogs/unreleased/52408-pip-cache-dir-to-cache-python-dependencies.yml

+---
+title: Use the standard PIP_CACHE_DIR for Python dependency caching template
+merge_request: 22211
+author: Takuya Noguchi
+type: fixed

doc/ci/caching/index.md

@@ -253,7 +253,7 @@ image: python:latest
 # Change pip's cache directory to be inside the project directory since we can
 # only cache local items.
 variables:
-    PIP_CACHE_DIR: "$CI_PROJECT_DIR/.cache"
+    PIP_CACHE_DIR: "$CI_PROJECT_DIR/.cache/pip"
 
 # Pip's cache doesn't store the python packages
 # https://pip.pypa.io/en/stable/reference/pip_install/#caching
@@ -262,7 +262,7 @@ variables:
 # them in a virtualenv and cache it as well.
 cache:
   paths:
-    - .cache/
+    - .cache/pip
     - venv/
 
 before_script:

lib/gitlab/ci/templates/Python.gitlab-ci.yml

@@ -5,7 +5,7 @@ image: python:latest
 # Change pip's cache directory to be inside the project directory since we can
 # only cache local items.
 variables:
-  PIP_CACHE_DIR: "$CI_PROJECT_DIR/.cache"
+  PIP_CACHE_DIR: "$CI_PROJECT_DIR/.cache/pip"
 
 # Pip's cache doesn't store the python packages
 # https://pip.pypa.io/en/stable/reference/pip_install/#caching