ci: pin `minreq` to `2.13.2`, `base64ct` to `1.6.0` for MSRV #6985

Job	Run time
prepare	5s
Check no_std	36s
Check WASM	1m 7s
Build & Test (1.84.1, true, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	43s
Build & Test Examples (example_cli)	38s
Build & Test (1.84.1, true, --all-features)	46s
Rust clippy	1m 19s
Build & Test Examples (example_bitcoind_rpc_polling)	51s
Build & Test (1.63.0, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	42s
Rust fmt	14s
Build & Test Examples (example_electrum)	54s
Build & Test (1.63.0, --all-features)	44s
Build & Test Examples (example_esplora)	1m 2s
Build & Test (1.75.0, --no-default-features --features miniscript/no-std,bdk_chain/hashbrown)	43s
Build & Test Examples (example_wallet_electrum)	56s
Build & Test (1.75.0, --all-features)	29s
Build & Test Examples (example_wallet_esplora_async)	1m 3s
Build & Test Examples (example_wallet_esplora_blocking)	53s
Build & Test Examples (example_wallet_rpc)	37s
	14m 22s

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