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/internal-functions

@@ -1,7 +1,8 @@
 #!/usr/bin/env bash
 source "$PLUGIN_CORE_AVAILABLE_PATH/common/functions"
 source "$PLUGIN_CORE_AVAILABLE_PATH/common/property-functions"
-set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
+set -eo pipefail
+[[ $DOKKU_TRACE ]] && set -x
 
 cmd-git-report() {
   declare desc="displays a git report for one or more apps"
@@ -46,7 +47,8 @@ cmd-git-report-single() {
       dokku_log_verbose "$(printf "%-30s %-25s" "${key^}" "${flag#*: }")"
     done
   else
-    local match=false; local value_exists=false
+    local match=false
+    local value_exists=false
     for flag in "${flag_map[@]}"; do
       valid_flags="${valid_flags} $(echo "$flag" | cut -d':' -f1)"
       if [[ "$flag" == "${INFO_FLAG}:"* ]]; then
@@ -66,7 +68,7 @@ cmd-git-report-single() {
 
 git_help_content_func() {
   declare desc="return git plugin help content"
-  cat<<help_content
+  cat <<help_content
     git:initialize <app>, Initialize a git repository for an app
     git:report [<app>] [<flag>], Displays a git report for one or more apps
     git:set <app> <property> (<value>), Set or clear a git property for an app
@@ -74,7 +76,7 @@ help_content
 }
 
 cmd-git-help() {
-  if [[ $1 = "git:help" ]] ; then
+  if [[ $1 == "git:help" ]]; then
     echo -e 'Usage: dokku git[:COMMAND]'
     echo ''
     echo 'Manages the git integration for an app.'
@@ -85,7 +87,7 @@ cmd-git-help() {
   elif [[ $(ps -o command= $PPID) == *"--all"* ]]; then
     git_help_content_func
   else
-    cat<<help_desc
+    cat <<help_desc
     git, Manages the git integration for an app
 help_desc
   fi