test: rename worker MessagePort test

All other tests for message ports use the `-` in between
`message` and `port`. This is annoying when using tab completion
for filenames.

PR-URL: #28024
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Yongsheng Zhang <[email protected]>
Reviewed-By: Richard Lau <[email protected]>
Reviewed-By: Trivikram Kamat <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>

Author: addaleax