Suppress cppcheck 1.89 false positive

Suppress cppcheck 1.89 false positive

cppcheck 1.89 emits a false positive for lib/isc/sha1.c:

    lib/isc/sha1.c:273:16: error: Uninitialized variable: block [uninitvar]
     (void)memmove(block, buffer, 64);
                   ^
    lib/isc/sha1.c:272:10: note: Assignment 'block=&workspace', assigned value is <Uninit>
     block = &workspace;
             ^
    lib/isc/sha1.c:273:16: note: Uninitialized variable: block
     (void)memmove(block, buffer, 64);
                   ^

This message started appearing with cppcheck 1.89 [1], but it will be
gone in the next release [2], so just suppress it for the time being.

[1] https://github.com/danmar/cppcheck/commit/af214e8212efa303e664920a468de00ee0b1fe3d

[2] https://github.com/danmar/cppcheck/commit/2595b826349a7ffbe1c958b806498b6e336bea33