🔧 fix: plain native static response

Author: SaltyAom

src/context.ts

@@ -134,7 +134,7 @@ export type Context<
 		redirect: Redirect
 
 		set: {
-			headers: HTTPHeaders
+		headers: HTTPHeaders
 			status?: number | keyof StatusMap
 			/**
 			 * @deprecated Use inline redirect instead

src/types.ts

@@ -1480,7 +1480,7 @@ export type HTTPHeaders = Record<string, string> & {
 
 	// Message body information
 	'content-length'?: string
-	'content-type'?: SetContentType | {}
+	'content-type'?: SetContentType | (string & {})
 	'content-encoding'?: string
 	'content-language'?: string
 	'content-location'?: string

test/core/native-static.test.ts

@@ -39,6 +39,7 @@ describe('Native Static Response', () => {
 
 		expect(app.router.static.http.static['/']).toBeInstanceOf(Response)
 		expect(app.router.static.http.static['/'].headers.toJSON()).toEqual({
+			'content-type': 'text/plain;charset=utf-8',
 			server: 'Elysia'
 		})
 		expect(await app.router.static.http.static['/'].text()).toEqual(
@@ -51,6 +52,7 @@ describe('Native Static Response', () => {
 		expect(
 			app.router.static.http.static['/plugin'].headers.toJSON()
 		).toEqual({
+			'content-type': 'text/plain;charset=utf-8',
 			server: 'Elysia'
 		})
 		expect(await app.router.static.http.static['/plugin'].text()).toEqual(