What does this PR aim to accomplish?:

Fixes pihole -t erroring out with /usr/local/bin/pihole: line 393: LOGFILE: readonly variable

Shellcheck does insist that variable declaration and variable assignment happen on two different lines but readonly variables need to be assigned first and then set as readonly

https://www.shellcheck.net/wiki/SC2155

Problematic code in the case of readonly:

readonly foo="$(mycmd)"

Correct code:

foo="$(mycmd)"
readonly foo

How does this PR accomplish the above?:

Flip declaration and readonly assignment.

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