Rename sourcemap files when renaming .mjs to .js

[westonruter]

This follows up on something I missed in 46aa70a (as part of #578). Namely, I saw in the console:

DevTools failed to load source map: Could not load content for .../pwa/wp-includes/js/workbox-v6.5.3/workbox-window.dev.js.map: HTTP error: status code 404, net::ERR_HTTP_RESPONSE_CODE_FAILURE

The issue is that when I renamed .mjs to .js I didn't also rename the .mjs.map to .js.map. This results in the following change to the build:

130c130
< ./wp-includes/js/workbox-v6.5.3/workbox-window.dev.es5.mjs.map
---
> ./wp-includes/js/workbox-v6.5.3/workbox-window.dev.es5.js.map
132c132
< ./wp-includes/js/workbox-v6.5.3/workbox-window.dev.mjs.map
---
> ./wp-includes/js/workbox-v6.5.3/workbox-window.dev.js.map
136c136
< ./wp-includes/js/workbox-v6.5.3/workbox-window.prod.es5.mjs.map
---
> ./wp-includes/js/workbox-v6.5.3/workbox-window.prod.es5.js.map
138c138
< ./wp-includes/js/workbox-v6.5.3/workbox-window.prod.mjs.map
---
> ./wp-includes/js/workbox-v6.5.3/workbox-window.prod.js.map

[codecov-commenter]

Codecov Report

Merging #777 (800a6ec) into develop (949d03d) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             develop     #777   +/-   ##
==========================================
  Coverage      19.01%   19.01%           
  Complexity       346      346           
==========================================
  Files             57       57           
  Lines           2324     2324           
==========================================
  Hits             442      442           
  Misses          1882     1882           

Flag	Coverage Δ
php	19.01% <ø> (ø)
unit	19.01% <ø> (ø)

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