fix: use absolute path for snapshot export dir to avoid test bootstrap crash

The test process working directory differs from the shell's, so a
relative path caused the SnapshotCIExportCoordinator to fail creating
the export directory, triggering a preconditionFailure (SIGTRAP) during
test bootstrapping.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: cameroncooke

.github/workflows/ios_sentry_upload_snapshots.yml

@@ -42,7 +42,7 @@ jobs:
 
       - name: Generate snapshot images (iPhone)
         run: |
-          set -o pipefail && TEST_RUNNER_SNAPSHOTS_EXPORT_DIR="snapshot-images/" xcodebuild test \
+          set -o pipefail && TEST_RUNNER_SNAPSHOTS_EXPORT_DIR="$PWD/snapshot-images" xcodebuild test \
             -scheme HackerNews \
             -sdk iphonesimulator \
             -destination 'platform=iOS Simulator,name=iPhone 17 Pro Max' \