ci: update rust stable to 1.78 and nightly 2024-05-15 #9099

Job	Run time
build-wasm (ubuntu-latest, v2, 2.4.0)	4m 36s
namada-release (ubuntu-latest, 2.4.0, ABCI Release build)	8m 6s
run-benchmarks (ubuntu-latest, nightly-2024-02-10, 2.4.0, ABCI)	31m 8s
test-unit (ubuntu-latest, nightly-2024-02-10, 2.4.0, ABCI)	21m 34s
test-wasm (ubuntu-latest, v2, nightly-2024-02-10, 2.4.0)	7m 56s
test-integration (ubuntu-latest, nightly-2024-02-10, 2.4.0, ABCI)	14m 46s
upload-wasm (ubuntu-latest, v2, nightly-2024-02-10, 2.4.0)	15s
namada-e2e (ubuntu-latest, nightly-2024-02-10, 2.4.0, 0.37.2, 0)	21m 18s
namada-e2e (ubuntu-latest, nightly-2024-02-10, 2.4.0, 0.37.2, 1)	11m 21s
namada-e2e (ubuntu-latest, nightly-2024-02-10, 2.4.0, 0.37.2, 2)	7m 55s
namada-e2e (ubuntu-latest, nightly-2024-02-10, 2.4.0, 0.37.2, 3)	25m 31s
namada-e2e (ubuntu-latest, nightly-2024-02-10, 2.4.0, 0.37.2, 4)	16m 19s
namada-e2e (ubuntu-latest, nightly-2024-02-10, 2.4.0, 0.37.2, 5)	20m 11s
	3h 10m 56s

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