fix: do not run npm --if-present build on npm cache hit

[achingbrain]

Fixes a regression introduced by #1070.

Essentially you can't include ${{ ... }} inside regular YAML if clauses, you have to have the whole clause inside ${{ ... }}.

This explains why every monorepo job builds on every run despite the npm/build cache being hit.

For the situation where the build cache exists (run GH action with debug logging turned on to see this sort of thing):

Before:

##[debug]Evaluating condition for step: 'run'
##[debug]Evaluating: (success() && format('steps.cache.outputs.cache-hit != ''true'' && {0} == ''true''', inputs.build_on_cache_fail))
##[debug]Evaluating And:
##[debug]..Evaluating success:
##[debug]..=> true
##[debug]..Evaluating format:
##[debug]....Evaluating String:
##[debug]....=> 'steps.cache.outputs.cache-hit != ''true'' && {0} == ''true'''
##[debug]....Evaluating Index:
##[debug]......Evaluating inputs:
##[debug]......=> Object
##[debug]......Evaluating String:
##[debug]......=> 'build_on_cache_fail'
##[debug]....=> 'true'
##[debug]..=> 'steps.cache.outputs.cache-hit != ''true'' && true == ''true'''
##[debug]=> 'steps.cache.outputs.cache-hit != ''true'' && true == ''true'''
##[debug]Expanded: (true && 'steps.cache.outputs.cache-hit != ''true'' && true == ''true''')
##[debug]Result: 'steps.cache.outputs.cache-hit != ''true'' && true == ''true'''
##[debug]Starting: run

Essentially it's evaluating (true && 'steps.cache.outputs.cache-hit != ''true'' && true == ''true'''), e.g. (true && string) which always evaluates to true.

After:

##[debug]Evaluating condition for step: 'run'
##[debug]Evaluating: (success() && (steps.cache.outputs.cache-hit != 'true') && (inputs.build_on_cache_fail == 'true'))
##[debug]Evaluating And:
##[debug]..Evaluating success:
##[debug]..=> true
##[debug]..Evaluating NotEqual:
##[debug]....Evaluating Index:
##[debug]......Evaluating Index:
##[debug]........Evaluating Index:
##[debug]..........Evaluating steps:
##[debug]..........=> Object
##[debug]..........Evaluating String:
##[debug]..........=> 'cache'
##[debug]........=> Object
##[debug]........Evaluating String:
##[debug]........=> 'outputs'
##[debug]......=> Object
##[debug]......Evaluating String:
##[debug]......=> 'cache-hit'
##[debug]....=> 'true'
##[debug]....Evaluating String:
##[debug]....=> 'true'
##[debug]..=> false
##[debug]=> false
##[debug]Expanded: (true && ('true' != 'true') && (inputs['build_on_cache_fail'] == 'true'))
##[debug]Result: false

[achingbrain]

This will shave 2-3 minutes off every linux job in the libp2p monorepo.

[achingbrain]

In this repo too, the npm install/build in CI for this PR took 57s the first time then 16s subsequently.