[ci] Escape + in grep string

Author: Dmitri Naumov

scripts/ci/extends/template-build-linux.yml

@@ -116,7 +116,7 @@
                                                          -e 'lto-wrapper: warning:' \
                                                          -e 'ld: warning:' \
                                                          -e "warning: 'has_denorm' is deprecated" \
-                                                         -e 'dlmalloc_ext_2_8_6\.c:[0-9:]+: warning: iteration [0-9]+ invokes undefined behavior' \
+                                                         -e 'dlmalloc_ext_2_8_6\.c:[0-9:]\+: warning: iteration [0-9]\+ invokes undefined behavior' \
                                                          -e '1 warning generated' \
                                                          ) || true
         if [[ -n $warnings ]]; then