[CI] Fix misspelled runtimes_targets variable (#167696)

This was preventing check-compiler-rt from actually running when we
touched a project that was supposed to cause compiler-rt to be tested.

Author: boomanaiden154

.ci/monolithic-windows.sh

@@ -55,7 +55,7 @@ start-group "ninja"
 ninja -C "${BUILD_DIR}" -k 0 ${targets} |& tee ninja.log
 cp ${BUILD_DIR}/.ninja_log ninja.ninja_log
 
-if [[ "${runtime_targets}" != "" ]]; then
+if [[ "${runtimes_targets}" != "" ]]; then
   start-group "ninja runtimes"
 
   ninja -C "${BUILD_DIR}" -k 0 ${runtimes_targets} |& tee ninja_runtimes.log