CI: Bump and ref actions by commit SHA in ci.yml

Referencing actions by commit SHA in GitHub workflows guarantees you are using an immutable version. Actions referenced by tags and branches are more vulnerable to attacks, such as the tag being moved to a malicious commit or a malicious commit being pushed to the branch.

It's important to make sure the SHA's are from the original repositories and not forks.

For reference:

https://github.com/actions/checkout/releases/tag/v4.1.0
8ade135a41

https://github.com/actions/upload-artifact/releases/tag/v3.1.3
a8a3f3ad30

Signed-off-by: Gabriela Gutierrez <gabigutierrez@google.com>

.github/workflows/ci.yml

@@ -27,7 +27,7 @@ jobs:
         build_system: [autotools, cmake]
     runs-on: ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608 #v4.1.0
 
       ########################
       # Install Dependencies #
@@ -135,7 +135,7 @@ jobs:
         run: ./build-aux/ci_build.sh -b ${{ matrix.build_system }} -d small -p test -n small
 
       # Attempt to upload the test logs as artifacts if any step has failed
-      - uses: actions/upload-artifact@v3
+      - uses: actions/upload-artifact@a8a3f3ad30e3422c9c7b888a15615d19a852ae32 #v3.1.3
         if: ${{ failure() }}
         with:
           name: ${{ matrix.os }} ${{ matrix.build_system }} Test Logs