Fix broken sourcemap output due to bad filename replacement

[markerikson]

Fixes #1704 , hopefully

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size-limit report 📦

Path	Size
1. entry point: @reduxjs/toolkit (cjs.production.min.js)	12.93 KB (0%)
1. entry point: @reduxjs/toolkit (esm.js)	10.79 KB (0%)
1. entry point: @reduxjs/toolkit/query (cjs.production.min.js)	22.55 KB (0%)
1. entry point: @reduxjs/toolkit/query (esm.js)	18.91 KB (0%)
1. entry point: @reduxjs/toolkit/query/react (cjs.production.min.js)	24.8 KB (0%)
1. entry point: @reduxjs/toolkit/query/react (esm.js)	21.6 KB (0%)
2. entry point: @reduxjs/toolkit (without dependencies) (cjs.production.min.js)	5.71 KB (0%)
2. entry point: @reduxjs/toolkit (without dependencies) (esm.js)	5.67 KB (0%)
2. entry point: @reduxjs/toolkit/query (without dependencies) (cjs.production.min.js)	10.01 KB (0%)
2. entry point: @reduxjs/toolkit/query (without dependencies) (esm.js)	10.43 KB (0%)
2. entry point: @reduxjs/toolkit/query/react (without dependencies) (cjs.production.min.js)	2.8 KB (0%)
2. entry point: @reduxjs/toolkit/query/react (without dependencies) (esm.js)	3.21 KB (0%)
3. createSlice (esm.js)	5.03 KB (0%)
3. createEntityAdapter (esm.js)	6.28 KB (0%)
3. configureStore (esm.js)	5.65 KB (0%)
3. createApi (esm.js)	17.14 KB (0%)
3. createApi (react) (esm.js)	19.84 KB (0%)
3. fetchBaseQuery (esm.js)	11.61 KB (0%)
3. setupListeners (esm.js)	10.42 KB (0%)
3. ApiProvider (esm.js)	18.47 KB (0%)