btrfs-progs: ci: calculate sha256 checksums for static binaries

Calculate checksums for static binaries that are published as release
artifacts. Do that when they're built in the workflow so the checksum
appears in the build log and also provide the artifacts of the checksums
so they can be published along the releases.

Signed-off-by: David Sterba <dsterba@suse.com>

.github/workflows/artifacts-static-build.yml

@@ -22,13 +22,27 @@ jobs:
         run: make V=1 btrfs.box.static
       - name: Strip binaries
         run: strip btrfs.static btrfs.box.static
+      - name: Calculate SHA256 checksums
+        run: |
+          sha256sum btrfs.static | tee btrfs.static.sha256
+          sha256sum btrfs.box.static | tee btrfs.box.static.sha256
       - name: Save artifacts - btrfs.static
         uses: actions/upload-artifact@v3
         with:
           name: btrfs.static
           path: btrfs.static
+      - name: Save artifacts - btrfs.static.sha256
+        uses: actions/upload-artifact@v3
+        with:
+          name: btrfs.static.sha256
+          path: btrfs.static.sha256
       - name: Save artifacts - btrfs.box.static
         uses: actions/upload-artifact@v3
         with:
           name: btrfs.box.static
           path: btrfs.box.static
+      - name: Save artifacts - btrfs.box.static.sha256
+        uses: actions/upload-artifact@v3
+        with:
+          name: btrfs.box.static.sha256
+          path: btrfs.box.static.sha256