composer.json: pin the php-code-coverage dependency (#1253)
composer.json: pin the php-code-coverage dependency (#1253)

Previously, we were not pinning the version of php-code-coverage, which
made it hard to disentangle real coverage changes from changes in the
behavior of the code coverage library. Historically, this has not been
a problem, because php-code-coverage was very stable. However, between
versions 9.2.10 and 9.2.13, there were several changes/regressions that
caused coverage changes.

Pinning avoids any ambiguity, and ensures that coverage changes in a
PR come _only_ from the PR code changes (unless we're explicitly
updating the php-code-coverage pinned version).
smrealms/smr,hemberger/smr,hemberger/smr,hemberger/smr,smrealms/smr,hemberger/smr,smrealms/smr