Issues with wget/apk in alpine:3.13.0 and up

As the title suggests there seems to be an issue with apk/wget when using alpine:3.13.0 and higher. I have a simple Dockerfile:
```
FROM alpine:3.15.0

ENV http_proxy http://igwng.m086:3128
ENV https_proxy http://igwng.m086:3128

RUN http_proxy=http://igwng.m086:3128 apk add wget
```
When you build this Dockerfile `docker build -f Dockerfile .`
```
[+] Building 21.2s (5/5) FINISHED
=> [internal] load build definition from Dockerfile 0.1s
=> => transferring dockerfile: 194B 0.0s
=> [internal] load .dockerignore 0.1s
=> => transferring context: 2B 0.0s
=> [internal] load metadata for docker.io/library/alpine:3.15.0 10.8s
=> CACHED [1/2] FROM docker.io/library/alpine:3.15.0@sha256:21a3deaa0d32a8057914f36584b5288d2e5ecc984380bc0118285c70fa8c9300 0.0s
=> ERROR [2/2] RUN http_proxy=http://igwng.m086:3128 apk add wget 10.3s
------
> [2/2] RUN http_proxy=http://igwng.m086:3128 apk add wget:
#5 0.241 fetch https://dl-cdn.alpinelinux.org/alpine/v3.15/main/x86_64/APKINDEX.tar.gz
#5 5.246 ERROR: https://dl-cdn.alpinelinux.org/alpine/v3.15/main: temporary error (try again later)
#5 5.246 WARNING: Ignoring https://dl-cdn.alpinelinux.org/alpine/v3.15/main: No such file or directory
#5 5.247 fetch https://dl-cdn.alpinelinux.org/alpine/v3.15/community/x86_64/APKINDEX.tar.gz
#5 10.25 ERROR: https://dl-cdn.alpinelinux.org/alpine/v3.15/community: temporary error (try again later)
#5 10.25 WARNING: Ignoring https://dl-cdn.alpinelinux.org/alpine/v3.15/community: No such file or directory
#5 10.25 ERROR: unable to select packages:
#5 10.25 wget (no such package):
#5 10.25 required by: world[wget]
------
executor failed running [/bin/sh -c http_proxy=http://igwng.m086:3128 apk add wget]: exit code: 1
```

However, downgrading to alpine:3.12.0 works:
```
[+] Building 12.0s (6/6) FINISHED
=> [internal] load build definition from Dockerfile 0.1s
=> => transferring dockerfile: 194B 0.0s
=> [internal] load .dockerignore 0.1s
=> => transferring context: 2B 0.0s
=> [internal] load metadata for docker.io/library/alpine:3.12.0 11.8s
=> [1/2] FROM docker.io/library/alpine:3.12.0@sha256:185518070891758909c9f839cf4ca393ee977ac378609f700f60a771a2dfe321 0.0s
=> CACHED [2/2] RUN http_proxy=http://igwng.m086:3128 apk add wget 0.0s
=> exporting to image 0.0s
=> => exporting layers 0.0s
=> => writing image sha256:b62d5de7aa35dfd4a4f9b87b69bdf1ff31e6e94e2083d6e18504d0731bc76d15 0.0s
```

I've done a couple of tests regarding proxy/restarting Docker and pretty much anything else you could find on the web, nothing helped. But maybe this is a DNS Issue:

```
docker run -it --env http_proxy=http://igwng.m086:3128 --env https_proxy=http://igwng.m086:3128 alpine:3.12.0 sh
Unable to find image 'alpine:3.12.0' locally
3.12.0: Pulling from library/alpine
df20fa9351a1: Already exists
Digest: sha256:185518070891758909c9f839cf4ca393ee977ac378609f700f60a771a2dfe321
Status: Downloaded newer image for alpine:3.12.0
/ # nslookup github.com
Server: 192.168.65.5
Address: 192.168.65.5:53

Non-authoritative answer:
Name: github.com
Address: 140.82.121.4

/ # exit
```
```

docker run -it --env http_proxy=http://igwng.m086:3128 --env https_proxy=http://igwng.m086:3128 alpine:3.15.0 sh
Unable to find image 'alpine:3.15.0' locally
3.15.0: Pulling from library/alpine
59bf1c3509f3: Already exists
Digest: sha256:21a3deaa0d32a8057914f36584b5288d2e5ecc984380bc0118285c70fa8c9300
Status: Downloaded newer image for alpine:3.15.0
/ # nslookup github.com
Server: 192.168.65.5
Address: 192.168.65.5:53

Non-authoritative answer:
Name: github.com
Address: 140.82.121.4

*** Can't find github.com: No answer

/ # exit
```