Add --exists-action option to git checkouts for pip (#3880)

* Add --exists-action option to git checkouts for pip

Fixes #3879

* Move pip option to workflow file

* Try again with wipe

* Restrict to Windows

* Revert "Restrict to Windows"

This reverts commit d5cbaac.

.github/workflows/test.yml

@@ -11,6 +11,7 @@ env:
   # opentelemetry-python-contrib which is compatible with these Core repo
   # changes.
   CONTRIB_REPO_SHA: 9ce1c26d2732dfbdadbb492fc38c562dcd08ed2e
+
   # This is needed because we do not clone the core repo in contrib builds anymore.
   # When running contrib builds as part of core builds, we use actions/checkout@v4 which
   # does not set an environment variable (simply just runs tox), which is different when
@@ -19,6 +20,9 @@ env:
   # from within the contrib build.
   CORE_REPO_SHA: ${{ github.sha }}
 
+  # See #3879 and https://pip.pypa.io/en/stable/cli/pip/#exists-action-option
+  PIP_EXISTS_ACTION: w
+
 jobs:
   build:
     env: