[test] Fix env vars in experimental benchmarks script. (#33232)

diff --git a/tools/internal_ci/linux/grpc_e2e_performance_gke_experiment.sh b/tools/internal_ci/linux/grpc_e2e_performance_gke_experiment.sh
index 3e24887..e716849 100755
--- a/tools/internal_ci/linux/grpc_e2e_performance_gke_experiment.sh
+++ b/tools/internal_ci/linux/grpc_e2e_performance_gke_experiment.sh
@@ -25,13 +25,13 @@
 GRPC_CORE_REPO=grpc/grpc
 GRPC_CORE_GITREF=master
 GRPC_DOTNET_REPO=grpc/grpc-dotnet
-GRPC_DOTNET_COMMIT=master
+GRPC_DOTNET_GITREF=master
 GRPC_GO_REPO=grpc/grpc-go
 GRPC_GO_GITREF=master
 GRPC_JAVA_REPO=grpc/grpc-java
 GRPC_JAVA_GITREF=master
 TEST_INFRA_REPO=grpc/test-infra
-TEST_INFRA_COMMIT=master
+TEST_INFRA_GITREF=master
 
 # This is to ensure we can push and pull images from gcr.io. We do not
 # necessarily need it to run load tests, but will need it when we employ
@@ -62,12 +62,12 @@
 if [[ "${KOKORO_GITHUB_COMMIT_URL%/*}" == "https://github.com/grpc/grpc/commit" ]]; then
     GRPC_CORE_COMMIT="${KOKORO_GIT_COMMIT}"
 else
-    GRPC_CORE_COMMIT="$(git ls-remote -h https://github.com/"${GRPC_CORE_REPO}".git "${GRPC_CORE_GITREF}" | cut -f1)"
+    GRPC_CORE_COMMIT="$(git ls-remote -h "https://github.com/${GRPC_CORE_REPO}.git" "${GRPC_CORE_GITREF}" | cut -f1)"
 fi
 
-GRPC_DOTNET_COMMIT="$(git ls-remote https://github.com/"${GRPC_DOTNET_REPO}".git "${GRPC_DOTNET_GITREF}" | cut -f1)"
-GRPC_GO_COMMIT="$(git ls-remote https://github.com/"${GRPC_GO_REPO}".git "${GRPC_GO_GITREF}" | cut -f1)"
-GRPC_JAVA_COMMIT="$(git ls-remote https://github.com/"${GRPC_JAVA_REPO}".git "${GRPC_JAVA_GITREF}" | cut -f1)"
+GRPC_DOTNET_COMMIT="$(git ls-remote "https://github.com/${GRPC_DOTNET_REPO}.git" "${GRPC_DOTNET_GITREF}" | cut -f1)"
+GRPC_GO_COMMIT="$(git ls-remote "https://github.com/${GRPC_GO_REPO}.git" "${GRPC_GO_GITREF}" | cut -f1)"
+GRPC_JAVA_COMMIT="$(git ls-remote "https://github.com/${GRPC_JAVA_REPO}.git" "${GRPC_JAVA_GITREF}" | cut -f1)"
 # Kokoro jobs run on dedicated pools.
 DRIVER_POOL=drivers-ci
 WORKER_POOL_8CORE=workers-c2-8core-ci
@@ -80,7 +80,7 @@
 mkdir ../test-infra
 pushd ../test-infra
 git clone "https://github.com/${TEST_INFRA_REPO}.git" .
-git checkout "${TEST_INFRA_COMMIT}"
+git checkout "${TEST_INFRA_GITREF}"
 make all-tools
 popd
 
@@ -125,12 +125,12 @@
 
 # Build and push prebuilt images for running tests.
 time ../test-infra/bin/prepare_prebuilt_workers \
-    -l "cxx:${GRPC_CORE_COMMIT}:${GRPC_CORE_COMMIT}" \
+    -l "cxx:${GRPC_CORE_REPO}:${GRPC_CORE_COMMIT}" \
     -l "dotnet:${GRPC_DOTNET_REPO}:${GRPC_DOTNET_COMMIT}" \
     -l "go:${GRPC_GO_REPO}:${GRPC_GO_COMMIT}" \
     -l "java:${GRPC_JAVA_REPO}:${GRPC_JAVA_COMMIT}" \
-    -l "python:${GRPC_CORE_COMMIT}:${GRPC_CORE_COMMIT}" \
-    -l "ruby:${GRPC_CORE_COMMIT}:${GRPC_CORE_COMMIT}" \
+    -l "python:${GRPC_CORE_REPO}:${GRPC_CORE_COMMIT}" \
+    -l "ruby:${GRPC_CORE_REPO}:${GRPC_CORE_COMMIT}" \
     -p "${PREBUILT_IMAGE_PREFIX}" \
     -t "${UNIQUE_IDENTIFIER}" \
     -r "${ROOT_DIRECTORY_OF_DOCKERFILES}"