esm: do not interpret "main" as a URL

[aduh95]

As documented, its value is a path.

node/doc/api/packages.md

Lines 1210 to 1211 in c42d846

	The `"main"` field defines the entry point of a package when imported by name
	via a `node_modules` lookup. Its value is a path.

[nodejs-github-bot]

Review requested:

• @nodejs/loaders

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.03%. Comparing base (c42d846) to head (f0c3a2c).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #55003   +/-   ##
=======================================
  Coverage   88.03%   88.03%           
=======================================
  Files         652      652           
  Lines      183759   183744   -15     
  Branches    35861    35853    -8     
=======================================
- Hits       161770   161766    -4     
+ Misses      15239    15229   -10     
+ Partials     6750     6749    -1     

Files with missing lines	Coverage Δ
lib/internal/modules/esm/resolve.js	96.62% <100.00%> (-0.01%)	⬇️
src/node_file.cc	77.36% <100.00%> (+0.26%)	⬆️

... and 31 files with indirect coverage changes