Add portmidi static library to dev package

As posted on mentors list, this is an MR to add libportmidi.a to the dev package.

Based on the file list for bookworm, it's still missing libporttime.a, but seeing commented out patches for that, I'm assuming it's not needed. https://packages.debian.org/bookworm/amd64/libportmidi-dev/filelist

Pipeline builds same master (all green, but repro fails). Debdiff shows only the static lib added:

Files in second .changes but not in first
-----------------------------------------
-rw-r--r--  root/root   /usr/lib/x86_64-linux-gnu/libportmidi.a

Control files of package libportmidi-dev: lines which differ (wdiff format)
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Installed-Size: [-269-] {+332+}

No differences were encountered between the control files of package libportmidi2

No differences were encountered between the control files of package libportmidi2-dbgsym

Note, I haven't done any serious checks beyond a quick sanity objdump of the static lib