cmake: Use requirements_lock_3_#.txt file (instead of requirements.in).

Fixes `build_and_test / ubuntu-latest cmake` failure as reported here:

* #25 (comment)

PiperOrigin-RevId: 644209740

scripts/build_and_run_tests_cmake.sh

@@ -71,7 +71,7 @@ function cleanup {
 trap cleanup EXIT
 
 echo -e "\e[33mInstalling the requirements (use --noinstall to skip).\e[0m"
-pip3 install --upgrade -r ./pybind11_abseil/requirements/requirements.in
+pip3 install --upgrade -r $(python3 -c 'import sys; print("./pybind11_abseil/requirements/requirements_lock_%d_%d.txt" % (sys.version_info[:2]))')
 
 echo "Building and testing in $PWD using 'python' (version $PYVERSION)."