PYTHON-5196 Use consistent secrets file name in oidc tests (#633)

Author: blink1073

.evergreen/auth_oidc/azure/remote-scripts/run-self-test.sh

@@ -3,6 +3,9 @@ set -o errexit
 set -o pipefail
 
 source env.sh
+# Copy the env.sh file to secrets-export.sh, but leave env.sh
+# for backwards compatibility.
+cp env.sh secrets-export.sh
 pushd ./drivers-evergreen-tools/.evergreen/auth_oidc
 . ./activate-authoidcvenv.sh