fix(nextjs): Correctly handle ts middleware files

[lforst]

Potentially/hopefully relates to #6815

s/js/ts/ in a place where js should be ts.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.82 KB (-0.01% 🔽)
@sentry/browser - ES5 CDN Bundle (minified)	61.47 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.5 KB (+0.02% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	54.77 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	20.22 KB (0%)
@sentry/browser - Webpack (minified)	66.17 KB (0%)
@sentry/react - Webpack (gzipped + minified)	20.24 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	47.51 KB (0%)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	26.73 KB (-0.02% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	25.02 KB (+0.01% 🔺)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	43.12 KB (-0.83% 🔽)
@sentry/replay - Webpack (gzipped + minified)	38.45 KB (-0.99% 🔽)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	60.35 KB (added)