ci: fix build docker image

[bondarslavik]

• fixed platforms
• removed one step with the build (added 2 tags in one build)

Before:

$ time docker run --rm --volume=$(PWD):/check:delegated  mstruebing/editorconfig-checker
WARNING: The requested image's platform (linux/amd64) does not match the detected host platform (linux/arm64/v8) and no specific platform was requested

________________________________________________________
Executed in    6.42 secs      fish           external
   usr time   40.33 millis    0.08 millis   40.25 millis
   sys time   23.14 millis    1.19 millis   21.95 millis

After:

$ time docker run --rm --volume=$(PWD):/check:delegated  bondarslavik/editorconfig-checker

________________________________________________________
Executed in    3.82 secs      fish           external
   usr time   32.96 millis   78.00 micros   32.88 millis
   sys time   22.06 millis  832.00 micros   21.23 millis

Tested on MacBook M1Pro