Added automated Cargo.toml upgrade CI (#7) #50

Job	Run time
Lint (ubuntu-latest, stable)	24s
Test (ubuntu-latest, default, stable)	32s
Lint (ubuntu-latest, beta)	20s
Test (ubuntu-latest, default, beta)	42s
Lint (ubuntu-latest, nightly)	16s
Test (ubuntu-latest, default, nightly)	35s
Lint (macos-latest, stable)	19s
Test (ubuntu-latest, serde_debugging, stable)	39s
Lint (macos-latest, beta)	23s
Lint (macos-latest, nightly)	19s
Test (ubuntu-latest, serde_debugging, beta)	44s
Test (ubuntu-latest, serde_debugging, nightly)	36s
Test (macos-latest, default, stable)	23s
Test (macos-latest, default, beta)	30s
Test (macos-latest, default, nightly)	31s
Test (macos-latest, serde_debugging, stable)	25s
Test (macos-latest, serde_debugging, beta)	36s
Test (macos-latest, serde_debugging, nightly)	31s
	8m 45s

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