tests: run mvdan/shfmt on test runs

While I do not agree with _every_ style change, this will force Dokku to have consistent formatting across all shell scripts, which is arguably a Good Thing™.

The command used to reprocess everything is:

```shell
shfmt -l -bn -ci -i 2 -w .
```

plugins/git/subcommands/initialize

@@ -1,11 +1,13 @@
 #!/usr/bin/env bash
 source "$PLUGIN_CORE_AVAILABLE_PATH/common/functions"
 source "$PLUGIN_AVAILABLE_PATH/git/functions"
-set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
+set -eo pipefail
+[[ $DOKKU_TRACE ]] && set -x
 
 git-initialize-cmd() {
   declare desc="initialize a git repository for an app"
-  local cmd="git:initialize" argv=("$@"); [[ ${argv[0]} == "$cmd" ]] && shift 1
+  local cmd="git:initialize" argv=("$@")
+  [[ ${argv[0]} == "$cmd" ]] && shift 1
   declare APP="$1"
   is_valid_app_name "$APP"