Relax some copybara transform regexes

This means that comments like `//copybara:media3-only` are now detected
(no space between `//` and `copybara`) which will ensure that lines like
this are correctly transformed for the media3 and exoplayer2 GitHub
repos:
https://github.com/google/ExoPlayer/blob/aa4e0080147fe76a6c0cca40b7eccdf45eb58028/library/effect/build.gradle#L33
PiperOrigin-RevId: 527919649

library/effect/build.gradle

@@ -29,7 +29,6 @@ android {
     }
 
     sourceSets {
-        androidTest.assets.srcDir '../test_data/src/test/assets/' //copybara:media3-only
         androidTest.assets.srcDir '../../testdata/src/test/assets/'
         test.assets.srcDir '../../testdata/src/test/assets/'
     }