Fix package workflow: add missing --os linux argument

ci/package.sh requires --os (linux|darwin) but both nightly.yml and
release.yml were calling it without --os, causing the build to fail
with 'Missing required argument'. Add --os linux to all 4 package
steps (amd64 + arm64 in each workflow).

.gitea/workflows/nightly.yml

@@ -34,6 +34,7 @@ jobs:
           cd "${GITHUB_WORKSPACE:-.}"
           ./ci/package.sh \
             --version nightly \
+            --os linux \
             --arch amd64 \
             --target-dir /home/dguiducci/.cache/skald-ci/target/release \
             --output dist/
@@ -43,6 +44,7 @@ jobs:
           cd "${GITHUB_WORKSPACE:-.}"
           ./ci/package.sh \
             --version nightly \
+            --os linux \
             --arch arm64 \
             --target-dir /home/dguiducci/.cache/skald-ci/target/aarch64-unknown-linux-gnu/release \
             --output dist/

.gitea/workflows/release.yml

@@ -64,6 +64,7 @@ jobs:
           cd "${GITHUB_WORKSPACE:-.}"
           ./ci/package.sh \
             --version "${{ steps.extract-version.outputs.version }}" \
+            --os linux \
             --arch amd64 \
             --target-dir /home/dguiducci/.cache/skald-ci/target/release \
             --output dist/
@@ -73,6 +74,7 @@ jobs:
           cd "${GITHUB_WORKSPACE:-.}"
           ./ci/package.sh \
             --version "${{ steps.extract-version.outputs.version }}" \
+            --os linux \
             --arch arm64 \
             --target-dir /home/dguiducci/.cache/skald-ci/target/aarch64-unknown-linux-gnu/release \
             --output dist/