Correctly set the docker image for `x86-64_musl`. #2180

Job	Run time
Flatpak	18m 17s
Macos (native_dyn)	8m 1s
Linux (native_static, focal)	10m 8s
Macos (native_static)	10m 23s
Linux (native_dyn, focal)	14m 52s
Macos (native_mixed)	7m 43s
Macos (iOS_arm64)	4m 26s
Macos (iOS_x86_64)	3m 1s
Macos (iOS_Mac_ABI)	4m 40s
Linux (native_mixed, focal)	6m 35s
Macos (macOS_arm64_static)	54s
Linux (wasm, focal)	10m 11s
Macos (macOS_arm64_mixed)	3m 34s
Linux (armv6_static, focal)	4m 22s
Macos (macOS_x86_64)	2m 44s
Linux (armv6_dyn, focal)	2m 33s
Linux (armv6_mixed, focal)	1m 53s
Linux (armv8_static, focal)	4m 35s
Linux (armv8_dyn, focal)	2m 25s
Linux (armv8_mixed, focal)	1m 24s
Linux (aarch64_static, focal)	4m 6s
Linux (aarch64_dyn, focal)	5m 45s
Linux (aarch64_mixed, focal)	1m 50s
Linux (aarch64_musl_static, focal)	5m 26s
Linux (aarch64_musl_dyn, focal)	5m 45s
Linux (aarch64_musl_mixed, focal)	1m 58s
Linux (x86-64_musl_static, focal)	4m 23s
Linux (x86-64_musl_mixed, focal)	1m 43s
Linux (i586_static, focal)	3m 28s
Linux (i586_dyn, focal)	2m 5s
Linux (android_arm, focal)	47m 21s
Linux (android_arm64, focal)	50m 18s
Linux (android_x86, focal)	3m 23s
Linux (android_x86_64, focal)	3m 15s
Linux (native_mixed, bionic)	2m 55s
Linux (aarch64_mixed, bionic)	1m 13s
Linux (win32_static, f35)	6m 4s
Linux (win32_dyn, f35)	3m 49s
	4h 37m 28s

Provide feedback