Fix packaging CI (#94)

Closes FerretDB/FerretDB#5379.

Author: AlekSi

.github/workflows/ferretdb_packages.yml

@@ -85,9 +85,9 @@ jobs:
             pg: 15
           # TODO https://github.com/microsoft/documentdb/issues/259
           - arch: arm64
-            package: rhel8
+            os: rhel8
           - arch: arm64
-            package: rhel9
+            os: rhel9
 
     name: .${{ matrix.package }} (${{ matrix.os }}, ${{ matrix.arch }}, Pg${{ matrix.pg }})
     runs-on: ${{ matrix.runner }}