Fix default log format to FormatRunner

What does this MR do?

In !4897 (merged), the format was wrongly defaulted to FormatText instead of FormatRunner.

This MR changes is to the right default value

Why was this MR needed?

To fix a bug introduced in !4897 (merged)

What's the best way to test this MR?

1. Start Runner using this branch
2. Log in the debug console should look like

Runtime platform                                    arch=arm64 os=darwin pid=77443 revision=HEAD version=development version
Starting multi-runner from /Users/ratchade/.gitlab-runner/config.windows-runner-2.toml...  builds=0 max_builds=0
Checking runtime mode                               GOOS=darwin uid=501
WARNING: Running in user-mode.                     
WARNING: Use sudo for system-mode:                 
WARNING: $ sudo gitlab-runner...                   
                                                  
Configuration loaded                                builds=0 max_builds=1

<...>

Waiting for stop signal                             builds=0 max_builds=1
listen_address not defined, metrics & debug endpoints disabled  builds=0 max_builds=1
[session_server].listen_address not defined, session endpoints disabled  builds=0 max_builds=1
Initializing executor providers                     builds=0 max_builds=1
Feeding runners to channel                          builds=0 max_builds=1
Feeding runner to channel                           builds=0 max_builds=1 runner=REDACTED
Starting worker                                     builds=0 max_builds=1 worker=0
Processing runner                                   builds=0 max_builds=1 runner=REDACTED
Acquiring executor from provider                    builds=0 max_builds=1 runner=REDACTED
Acquiring job slot                                  builds=0 max_builds=1 runner=REDACTED
Acquiring request slot                              builds=0 max_builds=1 runner=REDACTED
Dialing: tcp gitlab.com:443 ...                   
Checking for jobs...no content                      runner=REDACTED status=204 No Content
Feeding runners to channel                          builds=0 max_builds=1
Feeding runner to channel                           builds=0 max_builds=1 runner=REDACTED
Processing runner                                   builds=0 max_builds=1 runner=REDACTED
Acquiring executor from provider                    builds=0 max_builds=1 runner=REDACTED
Acquiring job slot                                  builds=0 max_builds=1 runner=REDACTED
Acquiring request slot                              builds=0 max_builds=1 runner=REDACTED
Feeding runners to channel                          builds=0 max_builds=1
Feeding runner to channel                           builds=0 max_builds=1 runner=REDACTED
Checking for jobs...no content                      runner=REDACTED status=204 No Content
Processing runner                                   builds=0 max_builds=1 runner=REDACTED
Acquiring executor from provider                    builds=0 max_builds=1 runner=REDACTED
Acquiring job slot                                  builds=0 max_builds=1 runner=REDACTED
Acquiring request slot                              builds=0 max_builds=1 runner=REDACTED
Feeding runners to channel                          builds=0 max_builds=1
Feeding runner to channel                           builds=0 max_builds=1 runner=REDACTED

What are the relevant issue numbers?