ci: use nested directories

Author: lqiu96

.github/workflows/downstream_protobuf_compatibility_check_nightly.yaml

@@ -63,7 +63,7 @@ jobs:
       - name: Print Protobuf-Java testing version
         run: echo "Testing with Protobuf-Java v${{ matrix.protobuf-version }}"
       - name: Perform downstream source compatibility testing
-        run: REPOS_UNDER_TEST="${{ matrix.repo }}" PROTOBUF_RUNTIME_VERSION="${{ matrix.protobuf-version}}" REPOS_INSTALLED_LOCALLY="true" ./.kokoro/nightly/downstream-protobuf-source-compatibility.sh
+        run: REPOS_UNDER_TEST="${{ matrix.repo }}" PROTOBUF_RUNTIME_VERSION="${{ matrix.protobuf-version }}" REPOS_INSTALLED_LOCALLY="true" ./.kokoro/nightly/downstream-protobuf-source-compatibility.sh
       - name: Perform downstream binary compatibility testing
-        run: REPOS_UNDER_TEST="${{ matrix.repo }}" PROTOBUF_RUNTIME_VERSION="${{ matrix.protobuf-version}}" REPOS_INSTALLED_LOCALLY="true" ./.kokoro/nightly/downstream-protobuf-binary-compatibility.sh
+        run: REPOS_UNDER_TEST="${{ matrix.repo }}" PROTOBUF_RUNTIME_VERSION="${{ matrix.protobuf-version }}" REPOS_INSTALLED_LOCALLY="true" ./.kokoro/nightly/downstream-protobuf-binary-compatibility.sh
 

.kokoro/nightly/downstream-protobuf-source-compatibility.sh

@@ -32,7 +32,7 @@ if [ -z "${PROTOBUF_RUNTIME_VERSION}" ]; then
 fi
 
 for repo in ${REPOS_UNDER_TEST//,/ }; do # Split on comma
-  if [ "${REPOS_INSTALLED}" != "true" ]; then
+  if [ "${REPOS_INSTALLED_LOCALLY}" != "true" ]; then
     # Perform source-compatibility testing on main (latest changes)
     git clone "https://github.com/googleapis/$repo.git" --depth=1
   fi