ci: remove `cc` pin to fix CI error #6754

Job	Run time
prepare	4s
Check no_std	47s
Check WASM	1m 17s
Build & Test Examples (example_cli)	41s
Build & Test (1.84.0, true, --no-default-features --features miniscript/no-std)	2m 54s
Build & Test Examples (example_bitcoind_rpc_polling)	46s
Rust clippy	1m 41s
Build & Test (1.84.0, true, --all-features)	4m 52s
Build & Test Examples (example_electrum)	1m 1s
Rust fmt	11s
Build & Test (1.63.0, --no-default-features --features miniscript/no-std)	6m 9s
Build & Test Examples (example_esplora)	1m 2s
Build & Test (1.63.0, --all-features)	6m 51s
Build & Test Examples (example_wallet_electrum)	58s
Build & Test (1.75.0, --no-default-features --features miniscript/no-std)	3m 9s
Build & Test Examples (example_wallet_esplora_async)	1m 5s
Build & Test (1.75.0, --all-features)	5m 11s
Build & Test Examples (example_wallet_esplora_blocking)	1m 1s
Build & Test Examples (example_wallet_rpc)	45s
	40m 25s

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