PYTHON-5615 Use uv python when python toolchain is not available (#2597)

Author: blink1073

.evergreen/combine-coverage.sh

@@ -5,19 +5,12 @@
 
 set -eu
 
-. .evergreen/utils.sh
+# Set up the virtual env.
+. .evergreen/scripts/setup-dev-env.sh
+uv sync --group coverage
+source .venv/bin/activate
 
-if [ -z "${PYTHON_BINARY:-}" ]; then
-    PYTHON_BINARY=$(find_python3)
-fi
-
-createvirtualenv "$PYTHON_BINARY" covenv
-# Keep in sync with run-tests.sh
-# coverage >=5 is needed for relative_files=true.
-pip install -q "coverage[toml]>=5,<=7.5"
-
-pip list
 ls -la coverage/
 
-python -m coverage combine coverage/coverage.*
-python -m coverage html -d htmlcov
+coverage combine coverage/coverage.*
+coverage html -d htmlcov

.evergreen/generated_configs/functions.yml

@@ -101,8 +101,8 @@ functions:
           - AUTH
           - SSL
           - ORCHESTRATION_FILE
-          - PYTHON_BINARY
-          - PYTHON_VERSION
+          - UV_PYTHON
+          - TOOLCHAIN_VERSION
           - STORAGE_ENGINE
           - REQUIRE_API_VERSION
           - DRIVERS_TOOLS
@@ -134,10 +134,10 @@ functions:
           - AWS_SECRET_ACCESS_KEY
           - AWS_SESSION_TOKEN
           - COVERAGE
-          - PYTHON_BINARY
+          - UV_PYTHON
           - LIBMONGOCRYPT_URL
           - MONGODB_URI
-          - PYTHON_VERSION
+          - TOOLCHAIN_VERSION
           - DISABLE_TEST_COMMANDS
           - GREEN_FRAMEWORK
           - NO_EXT