cli: only try to lint source files with --check

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/light-sheep-trade.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli': patch
+---
+
+Updated the ESLint plugin configuration that is enabled through `yarn start --check` to only pick up valid source files.

packages/cli/src/lib/bundler/config.ts

@@ -100,7 +100,7 @@ export async function createConfig(
       }),
       new ESLintPlugin({
         context: paths.targetPath,
-        files: ['**', '!**/__tests__/**', '!**/?(*.)(spec|test).*'],
+        files: ['**/*.(ts|tsx|mts|cts|js|jsx|mjs|cjs)'],
       }),
     );
   }
@@ -325,7 +325,7 @@ export async function createBackendConfig(
               typescript: { configFile: paths.targetTsConfig },
             }),
             new ESLintPlugin({
-              files: ['**', '!**/__tests__/**', '!**/?(*.)(spec|test).*'],
+              files: ['**/*.(ts|tsx|mts|cts|js|jsx|mjs|cjs)'],
             }),
           ]
         : []),