static-code-analysis/cppcheck: suppress unmatched suppressions

The cppcheck invocation without suppression of unmatched suppressions expects that there would be at least one error of suppressed kind. If there are none, cppcheck fails as well. This patch enables ignoring errors of that kind.

static-code-analysis.yml

 variables:
   RUN_FLAWFINDER: "flawfinder --falsepositive -m 4"
-  RUN_CPPCHECK: "cppcheck --enable=all --error-exitcode=1 --suppress=unusedFunction --suppress=unreadVariable ."
+  RUN_CPPCHECK: "cppcheck --enable=all --error-exitcode=1 --suppress=unusedFunction --suppress=unreadVariable --suppress=unmatchedSuppression ."
   RUN_CPD: "/home/user/pmd-bin-6.19.0/bin/run.sh cpd --minimum-tokens 200 --language c --exclude ./test/cmocka --files"
   SOURCE_FOLDER: "src"
   COMMON_IMAGE: "iopsys/code-analysis:0.27"