[Github] Default to non-root user in linux CI container (#119987)

This patch sets the default user in the linux CI container to a non-root
user, which enables properly testing a couple of features, particularly
in libcxx.

Author: boomanaiden154

.github/workflows/build-ci-container.yml

@@ -60,7 +60,7 @@ jobs:
       - name: Test Container
         run: |
           for image in ${{ steps.vars.outputs.container-name-tag }} ${{  steps.vars.outputs.container-name }}; do
-            podman run --rm -it $image /usr/bin/bash -x -c 'printf '\''#include <iostream>\nint main(int argc, char **argv) { std::cout << "Hello\\n"; }'\'' | clang++ -x c++ - && ./a.out | grep Hello'
+            podman run --rm -it $image /usr/bin/bash -x -c 'cd $HOME && printf '\''#include <iostream>\nint main(int argc, char **argv) { std::cout << "Hello\\n"; }'\'' | clang++ -x c++ - && ./a.out | grep Hello'
           done
 
   push-ci-container:

.github/workflows/containers/github-action-ci/Dockerfile

@@ -68,3 +68,10 @@ RUN apt-get update && \
 
 ENV LLVM_SYSROOT=$LLVM_SYSROOT
 ENV PATH=${LLVM_SYSROOT}/bin:${PATH}
+
+# Create a new user to avoid test failures related to a lack of expected
+# permissions issues in some tests. Set the user id to 1001 as that is the
+# user id that Github Actions uses to perform the checkout action.
+RUN useradd gha -u 1001 -m -s /bin/bash
+USER gha
+