Fix CI: json-c for crun, and fetch crun's git submodules as pinned tarballs

Verified end-to-end with a full local build of all 8 packages on the
actual runner host (docker exec against vbatts/slackware:15.0, bind-
mounted repo on the cache pool) instead of round-tripping through
Gitea Actions for each fix — much faster for a chain of issues this
deep. All 8 packages now build successfully from a clean checkout.

Three fixes, all in crun (the last package still failing):

1. "Package requirements (json-c >= 0.14) were not met" — added
   json-c to the toolchain bootstrap.

2. crun depends on the libocispec git submodule, which in turn depends
   on the image-spec and runtime-spec git submodules. GitHub's source
   archive tarball never includes submodule content (no .git directory
   for `git submodule update` to work against — the existing `|| true`
   masked this failing silently). Fetched all three as their own
   pinned tarballs instead, at the exact commits crun 1.28 references
   (cross-checked via the GitHub contents API), matching how every
   other dependency in this project is already pinned.

3. crun.c unconditionally #includes git-version.h, which crun's own
   Makefile only generates via `git describe` (again, no .git) or from
   a pre-existing .tarball-git-version.h — the file crun's own `make
   dist` would have written, which we never run. Write that file
   ourselves in the exact format the Makefile already expects; this is
   the documented fallback path bundled release tarballs rely on, not
   a workaround around it.

Also includes the podman go-md2man pre-seed fix and setup-slackware-
buildenv.sh python3 addition from the previous commit's follow-up
testing (both already verified working in this same local build run).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

packages/podman/podman.SlackBuild

@@ -50,6 +50,18 @@ export BUILDTAGS="seccomp exclude_graphdriver_btrfs exclude_graphdriver_devicema
 export CGO_ENABLED=1
 export GOFLAGS="${GOFLAGS:--mod=mod}"
 
+# podman's own Makefile wants to build ITS bundled copy of go-md2man from
+# test/tools/vendor/ for doc generation, but that vendor tree isn't
+# consistent enough to build standalone outside podman's own module scope
+# ("without -mod=vendor, directory ... has no package path"). Its Makefile
+# only attempts that build if test/tools/build/go-md2man doesn't already
+# exist — pre-seed it with our own system go-md2man (installed in
+# scripts/ci/setup-slackware-buildenv.sh) to skip the broken vendor build
+# entirely; it's the same tool doing the same job.
+mkdir -p test/tools/build
+cp "$(command -v go-md2man)" test/tools/build/go-md2man
+chmod +x test/tools/build/go-md2man
+
 echo "==> [podman] make (BUILDTAGS=$BUILDTAGS)"
 make BUILDTAGS="$BUILDTAGS" GO_BUILD_FLAGS="-ldflags -s"