[Bug] --registry-mirror does not work with warmer since v1.21.0

Actual behavior

It does not work with v1.21.0 or v1.22.0:

$ docker run gcr.nju.edu.cn/kaniko-project/warmer:v1.21.0 \
    --registry-mirror=docker.nju.edu.cn \
    --skip-default-registry-fallback \
    --image=python:3.11 \
    --verbosity=trace
DEBU[0000] /cache                                       
DEBU[0000] [python:3.11]                                
INFO[0000] Retrieving image manifest python:3.11
INFO[0000] Retrieving image python:3.11 from registry index.docker.io
WARN[0003] Error while trying to warm image: python:3.11 Failed to retrieve image: python:3.11: unable to complete operation after 0 attempts, last error: Get "https://index.docker.io/v2/": EOF 
WARN[0003] Error while trying to warm image: python:3.11 Failed to retrieve image: python:3.11: unable to complete operation after 0 attempts, last error: Get "https://index.docker.io/v2/": EOF 
Failed warming cache: Failed to warm any of the given images

Expected behavior

It works with v1.20.0 or older:

$ docker run gcr.nju.edu.cn/kaniko-project/warmer:v1.20.0 \
    --registry-mirror=docker.nju.edu.cn \
    --skip-default-registry-fallback \
    --image=python:3.11 \
    --verbosity=trace
DEBU[0000] /cache
DEBU[0000] [python:3.11]
INFO[0000] Retrieving image manifest python:3.11
INFO[0000] Retrieving image library/python:3.11 from registry mirror docker.nju.edu.cn
DEBU[0000] No file found for cache key sha256:21d1a3d86b1656a745a9ccfdd3a0797a694c9d48450e65734127183506a38e8c stat /cache/sha256:21d1a3d86b1656a745a9ccfdd3a0797a694c9d48450e65734127183506a38e8c: no such file or directory
DEBU[0001] Wrote python:3.11 to cache

To Reproduce Steps to reproduce the behavior:

As shown above.

Additional Information None

Triage Notes for the Maintainers

Description	Yes/No
Please check if this a new feature you are proposing	- [ ]
Please check if the build works in docker but not in kaniko	- [ ]
Please check if this error is seen when you use `--cache` flag	- [ ]
Please check if your dockerfile is a multistage dockerfile	- [ ]

GoogleContainerTools / kaniko

[Bug] --registry-mirror does not work with warmer since v1.21.0 #3134