Fix ~git/.ssh/environment file owner problem using in docker.

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Describe the pull request

I thought that you want to use gosu "$USER" echo "GOGS_CUSTOM=${GOGS_CUSTOM}" > ~git/.ssh/environment to create a ~git/.ssh/environment file owned by $USER and then write something to it when the s6 boots gogs service in a docker container. This gosu command is located in here.

But this command will actually create a ~git/.ssh/environment file owned by root:root. Because on the right side of the pip, the ~git/.ssh/environment is actually created by the current user (root), not $USER.

To have it the right owner (maybe git:git) the file should be touch (created) by $USER before use it. That is what I do.

Link to the issue: n/a

Checklist

• I agree to follow the Code of Conduct by submitting this pull request.
• I have read and acknowledge the Contributing guide.
• I have added test cases to cover the new code or have provided the test plan.

Test plan

You can test the code inside a gogs docker container by running these bash commands:

USER=git
gosu "$USER" touch ~git/.ssh/environment_test
gosu "$USER" echo "GOGS_CUSTOM=${GOGS_CUSTOM}" > ~git/.ssh/environment_test

Below is what I tested:

ba2e12b10e0f:/data/git# USER=git
ba2e12b10e0f:/data/git# gosu "$USER" touch ~git/.ssh/environment_test
ba2e12b10e0f:/data/git# gosu "$USER" echo "GOGS_CUSTOM=${GOGS_CUSTOM}" > ~git/.ssh/environment_test
ba2e12b10e0f:/data/git# ls -l ~git/.ssh/environment_test 
-rw-r--r--    1 git      git             23 Nov 11 16:09 /data/git/.ssh/environment_test

Besides, inside the same container, you can find the ~git/.ssh/environment file is owned by root:root ls -l ~git/.ssh/environment.