Bump rexml from 3.2.5 to 3.2.8 #7613

Job	Run time
spm-binary-cron	0s
changes	4s
check	1m 45s
cmake (macos-14)	15m 43s
cmake-prod-db (macos-14, (default))	13m 11s
cmake (ubuntu-latest)	16m 27s
cmake-prod-db (macos-14, test-db)	13m 19s
pod-lib-lint (FirebaseFirestoreInternal.podspec)	24m 5s
pod-lib-lint-cron	0s
pod-lib-lint (FirebaseFirestore.podspec)	29m 17s
sanitizers-mac (macos-14, asan)	13m 11s
sanitizers-ubuntu (ubuntu-latest, asan)	18m 5s
sanitizers-mac (macos-14, tsan)	15m 21s
spm-source (iOS, macos-13)	18m 19s
xcodebuild (iOS)	24m 14s
spm-source (iOS, macos-14)	15m 53s
xcodebuild (macOS)	23m 47s
spm-source (tvOS, macos-13)	16m 32s
xcodebuild (tvOS)	25m 26s
check-firestore-internal-public-headers	6s
spm-source (tvOS, macos-14)	13m 14s
spm-source (macOS, macos-13)	14m 35s
spm-source (macOS, macos-14)	13m 1s
spm-binary	3m 4s
spm-source (macos-14, visionOS, Xcode_15.3)	13m 50s
Check all required Firestore tests results	1s
	5h 42m 30s

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