soroban-cli: Only Give RC SDK Contract Compilation Warning/Errors if Using Pubnet #2991

Job	Run time
Build (ubuntu-latest, x86_64-unknown-linux-gnu, amd64)	2m 6s
Integration tests (ubuntu-20.04, 1.21, .CLI.)	17m 52s
Build (ubuntu-latest, aarch64-unknown-linux-gnu, arm64)	2m 31s
Integration tests (ubuntu-20.04, 1.21, ^Test(([^C])\|(C[^L])\|(CL[^I])).*$)	16m 16s
Build (macos-latest, x86_64-apple-darwin, amd64)	5m 0s
Build (macos-latest, aarch64-apple-darwin, arm64)	5m 1s
Unit tests (ubuntu-20.04, 1.21)	5m 56s
Build (windows-latest, x86_64-pc-windows-gnu, amd64)	5m 37s
	1h 0m 19s

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