Set locale command fails in the dockerfile

[jeffwidman]

Here we try to set LC_ALL: https://github.com/dependabot/dependabot-core/blob/58fd7492c025164874a941feafb11cc81f29b271/Dockerfile#L10

However, in the actual output of the build, I see the following errors:

1. https://github.com/dependabot/dependabot-core/runs/7646741836?check_suite_focus=true#step:3:148

/bin/bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)

2. https://github.com/dependabot/dependabot-core/runs/7646741836?check_suite_focus=true#step:3:186

#5 7.344 perl: warning: Setting locale failed.
#5 7.344 perl: warning: Please check that your locale settings:
#5 7.344 	LANGUAGE = (unset),
#5 7.344 	LC_ALL = "en_US.UTF-8",
#5 7.344 	LANG = "en_US.UTF-8"
#5 7.344     are supported and installed on your system.
#5 7.344 perl: warning: Falling back to the standard locale ("C").

3. https://github.com/dependabot/dependabot-core/runs/7646741836?check_suite_focus=true#step:3:1988

#5 58.21 Setting up ucf (3.0038+nmu1) ...
#5 58.26 locale: Cannot set LC_CTYPE to default locale: No such file or directory
#5 58.26 locale: Cannot set LC_MESSAGES to default locale: No such file or directory
#5 58.26 locale: Cannot set LC_ALL to default locale: No such file or directory

this final set of error messages repeats multiple times...

5. Then way down at the bottom I see this: https://github.com/dependabot/dependabot-core/runs/7646741836?check_suite_focus=true#step:3:2261

#5 70.78 /bin/bash: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)
#5 70.79 Generating locales (this might take a while)...
#5 70.79   en_US.UTF-8... done
#5 72.73 Generation complete.

I don't know enough about locales and debian to know if this might be resolved if we simply flipped the order to first generate the locale and then tried to set it?