oss-fuzz: Copy proj.db and additional data files to output directory

[am009]

When fuzzing, it frequently reports that proj.db is not found:

proj_create: Cannot find proj.db

The proj.db is generated under build/data, not data/.

[rouault]

@am009 Your fix looks plausible, but can you explain how you detected the issue and how you verified your PR fixes it ? Looking at a run of ci-fuzz on another pull request (https://github.com/OSGeo/PROJ/actions/runs/20169922244/job/57902633665?pr=4603), I don't see a "Cannot find proj.db" trace (but I'm aware the run might not be long enough to trigger it)

[am009]

This script was copied verbatim into FuzzBench, and I encountered this issue there. In FuzzBench, the build environment and the execution environment are separated, and only the $OUT directory is copied into the isolated runtime environment; as a result, proj.db cannot be found.

I am not very familiar with the OSS-Fuzz architecture, but it seems that its build and runtime environments may be the same. The preceding make install command in the script installs proj.db into the system, so proj.db can be located correctly.

sorry for opening this pull request without a thorough analysis. Based on the logs you provided, the issue indeed does not appear to exist. In that case, whether this fix is applied does not seem to matter much.