Ignore cppcheck syntax errors related to prevector

Summary:
These false positives can be safely ignored since the build system does not complain about
the supposed syntax errors.

A newer version of cppcheck is not available via buster-backports, so it's best that we ignore this
error until a version becomes available that fixes this issue.

Test Plan:

arc lint src/bench/prevector.cpp
arc lint src/test/prevector_tests.cpp

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D7140