Fix Bad substitution in Linux container builds

${GITHUB_SHA::8} is a bashism that fails under dash (default sh in
Ubuntu 20.04 containers). Use POSIX-compatible cut instead.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: wesm

.github/workflows/release.yml

@@ -53,7 +53,7 @@ jobs:
           VERSION=${GITHUB_REF#refs/tags/v}
 
           mkdir -p dist
-          LDFLAGS="-s -w -X github.com/wesm/msgvault/cmd/msgvault/cmd.Version=v${VERSION} -X github.com/wesm/msgvault/cmd/msgvault/cmd.Commit=${GITHUB_SHA::8} -X github.com/wesm/msgvault/cmd/msgvault/cmd.BuildDate=$(date -u +%Y-%m-%dT%H:%M:%SZ) -extldflags '-lstdc++ -lm'"
+          LDFLAGS="-s -w -X github.com/wesm/msgvault/cmd/msgvault/cmd.Version=v${VERSION} -X github.com/wesm/msgvault/cmd/msgvault/cmd.Commit=$(echo $GITHUB_SHA | cut -c1-8) -X github.com/wesm/msgvault/cmd/msgvault/cmd.BuildDate=$(date -u +%Y-%m-%dT%H:%M:%SZ) -extldflags '-lstdc++ -lm'"
           go build -tags fts5 -trimpath -buildvcs=false -ldflags="$LDFLAGS" -o dist/msgvault ./cmd/msgvault
 
           echo "--- Binary info ---"
@@ -106,7 +106,7 @@ jobs:
           VERSION=${GITHUB_REF#refs/tags/v}
 
           mkdir -p dist
-          LDFLAGS="-s -w -X github.com/wesm/msgvault/cmd/msgvault/cmd.Version=v${VERSION} -X github.com/wesm/msgvault/cmd/msgvault/cmd.Commit=${GITHUB_SHA::8} -X github.com/wesm/msgvault/cmd/msgvault/cmd.BuildDate=$(date -u +%Y-%m-%dT%H:%M:%SZ)"
+          LDFLAGS="-s -w -X github.com/wesm/msgvault/cmd/msgvault/cmd.Version=v${VERSION} -X github.com/wesm/msgvault/cmd/msgvault/cmd.Commit=$(echo $GITHUB_SHA | cut -c1-8) -X github.com/wesm/msgvault/cmd/msgvault/cmd.BuildDate=$(date -u +%Y-%m-%dT%H:%M:%SZ)"
           go build -tags fts5 -trimpath -ldflags="$LDFLAGS" -o dist/msgvault ./cmd/msgvault
 
           echo "--- Binary info ---"
@@ -162,7 +162,7 @@ jobs:
           VERSION="${GITHUB_REF#refs/tags/v}"
 
           mkdir -p dist
-          LDFLAGS="-s -w -X github.com/wesm/msgvault/cmd/msgvault/cmd.Version=v${VERSION} -X github.com/wesm/msgvault/cmd/msgvault/cmd.Commit=${GITHUB_SHA::8} -X github.com/wesm/msgvault/cmd/msgvault/cmd.BuildDate=$(date -u +%Y-%m-%dT%H:%M:%SZ)"
+          LDFLAGS="-s -w -X github.com/wesm/msgvault/cmd/msgvault/cmd.Version=v${VERSION} -X github.com/wesm/msgvault/cmd/msgvault/cmd.Commit=$(echo $GITHUB_SHA | cut -c1-8) -X github.com/wesm/msgvault/cmd/msgvault/cmd.BuildDate=$(date -u +%Y-%m-%dT%H:%M:%SZ)"
           go build -tags fts5 -trimpath -ldflags="$LDFLAGS" -o dist/msgvault.exe ./cmd/msgvault
 
           # Smoke test