Specify that Git branch names must be prefixed with a four-digit Redmine
issue number.

Don't output the Curl progress bar which can be jarring since you're not
expecting it.

When I ran this code I got the following error:

    Warning: You can only select one HTTP request method! You asked for both POST
    Warning: (-d, --data) and HEAD (-I, --head).
    redprine: error: Redmine API error, status code

Looks like in order to make my PUT request I need to get rid of the
'only headers' flag.

I changed that function around in
3c451d5f504c9872e4b589c998d52479f38aabbc such that now it gets called
directly by `update_redmine_status`, so we need to remove it here. Also
this line caused an error because the function was renamed.

We had initialised the `$CACHE_FILE` variable at the start of the script,
but because at that point `$GITHUB_OWNER_REPO` is empty, the cache file
just ends up getting called ".json".

In order to get the name we want, we need to wait until the
`$GITHUB_OWNER_REPO` variable is initialised by the command line
argument.

Initialise `$CACHE_FILE` in `preflight()` because it makes sense to put
it in that kind of setup function. Move `preflight()` after
`parse_arguments()` to ensure the program variables (including
`$GITHUB_OWNER_REPO`) are properly validated and initialised before
running setup code.

If this command line argument was passed, the program would go into an
infinite loop, prevented from finishing argument parsing.

When I switched this over to use the variable, I forgot to retain the
double quotes around the username string required by `jq`. Add these in
so that the username can be parsed as a properly quoted string.