Ignore `NO_COLOR` if set to empty string #2382

Job	Run time
Rustfmt and clippy	31s
Test (x86_64-unknown-linux-gnu, ubuntu-latest, --features=native-tls)	40s
Test (x86_64-unknown-linux-gnu, ubuntu-latest, --no-default-features --features=native-tls,online...	40s
Test (x86_64-apple-darwin, macos-13, --features=native-tls)	1m 42s
Test (aarch64-apple-darwin, macos-14, --features=native-tls)	58s
Test (x86_64-pc-windows-msvc, windows-latest, --features=native-tls)	1m 56s
Test (x86_64-unknown-linux-musl, ubuntu-latest, true)	1m 13s
Test (aarch64-unknown-linux-musl, ubuntu-latest, true, -- --test-threads=4)	1m 42s
Test (arm-unknown-linux-gnueabihf, ubuntu-latest, true, -- --test-threads=4)	1m 33s
	10m 55s

Provide feedback