ci: fetch legacy repo history so pre-migration sync SHAs resolve

Packages synced to OBS before the migration from
rjd15372/percona-obs-packaging to percona/obs-packaging carry sync
comments like 'sync: main@6f95b5a (rjd15372/...)' whose SHAs come from the
legacy repo's rebased history and do not exist in a percona-only clone.
The branch-decision/skip fast path runs git log <sha>..HEAD per package, so
an unresolvable SHA conservatively falls through to the full content check:
every PR run re-ran services for essentially the whole tree (~10 min), and
it also exposed the vendor.tar.gz drift promotions on PR #5.

The two histories share ancestry up to the migration point, so simply
fetching the legacy refs makes the old SHAs resolvable and the range
queries correct: verified in a percona-only clone that after the fetch
6f95b5a..HEAD is empty for untouched packages (fast aggregate) and still
lists the PR commits for packages the PR really changed.

The fetch is fail-open (warning only) and should be dropped once all
packages have been re-synced with percona/obs-packaging SHAs in their
comments.

Signed-off-by: Ricardo Dias <ricardo.dias@percona.com>

Author: rjd15372

.github/workflows/obs-pr-check.yml

@@ -120,6 +120,18 @@ jobs:
           # per package to detect which packages changed since main's last sync.
           fetch-depth: 0
 
+      # Packages synced before the migration to percona/obs-packaging carry
+      # OBS sync comments whose SHAs come from the legacy repo's history and
+      # do not resolve in this clone, which forces the branch decision off
+      # the cheap git gate into a full content check for every such package.
+      # Fetch the legacy history so those SHAs resolve; drop this step once
+      # all packages have been re-synced with percona/obs-packaging SHAs.
+      - name: Fetch legacy repo history (pre-migration sync SHAs)
+        run: |
+          git fetch https://github.com/rjd15372/percona-obs-packaging.git \
+            'refs/heads/*:refs/remotes/legacy/*' \
+            || echo "::warning::legacy repo unreachable; sync falls back to content checks"
+
       # Persists the content-addressed .cache/ tree across runs, split in
       # two entries (same layout as sync-main.yml so PR runs can restore the
       # main branch's caches via restore-keys):

.github/workflows/sync-main.yml

@@ -42,6 +42,18 @@ jobs:
           fetch-depth: 0
           token: ${{ secrets.GH_PAT }}
 
+      # Packages synced before the migration to percona/obs-packaging carry
+      # OBS sync comments whose SHAs come from the legacy repo's history and
+      # do not resolve in this clone, which forces --skip-unchanged off the
+      # cheap git gate into services + upload comparison for every such
+      # package.  Fetch the legacy history so those SHAs resolve; drop this
+      # step once all packages have been re-synced with percona SHAs.
+      - name: Fetch legacy repo history (pre-migration sync SHAs)
+        run: |
+          git fetch https://github.com/rjd15372/percona-obs-packaging.git \
+            'refs/heads/*:refs/remotes/legacy/*' \
+            || echo "::warning::legacy repo unreachable; sync falls back to content checks"
+
       # Persists the content-addressed .cache/ tree across runs, split in
       # two entries:
       #