When the `Json` strategy was introduced, I forgot to also ensure
that it's only treated as usable (in `Strategy#from_url`) if a
`livecheck` block uses `strategy :json`. As a result, `Json` is
incorrectly treated as a usable strategy for all formulae/casks that
contain a `strategy` block.
Since all of these `livecheck` blocks specify a strategy, this bug
doesn't meaningfully impact livecheck's behavior (i.e., these checks
continue to use their explicitly-specified strategy). The only
practical difference is that `Json` incorrectly appears in the list
of usable strategies in livecheck's verbose JSON output.
This commit modifies `Strategy#from_url` to address this issue. The
easiest way to enforce this rule involved passing in the
`@strategies` key (a symbol) into the `select` block, so we can
compare it to `livecheck_strategy` (the strategy symbol specified in
the `livecheck` block).
03823b5698