improve healthy() check for node

[asottile]

See pre-commit/action#45

for language_version: system hooks this looks like:

eslint...................................................................Failed
- hook id: eslint
- exit code: 127

/home/runner/.cache/pre-commit/repoibq27hfw/node_env-system/bin/node: line 5: /opt/hostedtoolcache/node/14.8.0/x64/bin/node: No such file or directory
/home/runner/.cache/pre-commit/repoibq27hfw/node_env-system/bin/node: line 5: /opt/hostedtoolcache/node/14.8.0/x64/bin/node: No such file or directory

##[error]The process '/opt/hostedtoolcache/Python/3.8.5/x64/bin/pre-commit' failed with exit code 1