Problem

Test will fail CI until a full srfit release is available so i pinned the rc release in CI.

Proposed solution

When a full srfit release is available (3.4.0), remove the following from matrix-and-codecov-on-merge-to-main.yml and tests-on-pr.yml

      run: |
        set -Eeuo pipefail
        python -m pip install --no-deps diffpy.srfit==3.4.0rc0