Enable lexical-binding in all test files

This is required by buttercup, and a hard error with buttercup >= 1.34
and Emacs >= 29.1.

tests/unit/test-webpaste-default-post-field-lambda.el

@@ -1,4 +1,4 @@
-;;; test-webpaste-default-post-field-lambda.el --- Tests for webpaste
+;;; test-webpaste-default-post-field-lambda.el --- Tests for webpaste -*- lexical-binding: t; -*-
 ;;; Commentary:
 ;;; Code:
 

tests/unit/test-webpaste-error-lambdas.el

@@ -1,4 +1,4 @@
-;;; test-webpaste-error-lambdas.el --- Tests for error lambdas
+;;; test-webpaste-error-lambdas.el --- Tests for error lambdas -*- lexical-binding: t; -*-
 ;;; Commentary:
 ;;; Code:
 

tests/unit/test-webpaste-get-language.el

@@ -1,4 +1,4 @@
-;;; test-webpaste-get-language.el --- Tests for webpaste
+;;; test-webpaste-get-language.el --- Tests for webpaste -*- lexical-binding: t; -*-
 ;;; Commentary:
 ;;; Code:
 

tests/unit/test-webpaste-get-provider-priority.el

@@ -1,4 +1,4 @@
-;;; test-webpaste-get-provider-priority.el --- Tests for webpaste
+;;; test-webpaste-get-provider-priority.el --- Tests for webpaste -*- lexical-binding: t; -*-
 ;;; Commentary:
 ;;; Code:
 

tests/unit/test-webpaste-paste-region-and-buffer.el

@@ -1,4 +1,4 @@
-;;; test-webpaste-paste-region-and-buffer.el --- Tests for webpaste
+;;; test-webpaste-paste-region-and-buffer.el --- Tests for webpaste -*- lexical-binding: t; -*-
 ;;; Commentary:
 ;;; Code:
 

tests/unit/test-webpaste-paste-text.el

@@ -1,4 +1,4 @@
-;;; test-webpaste-paste-text.el --- Tests for webpaste
+;;; test-webpaste-paste-text.el --- Tests for webpaste -*- lexical-binding: t; -*-
 ;;; Commentary:
 ;;; Code:
 

tests/unit/test-webpaste-provider-creation.el

@@ -1,4 +1,4 @@
-;;; test-webpaste-provider-creation.el --- Tests for webpaste
+;;; test-webpaste-provider-creation.el --- Tests for webpaste -*- lexical-binding: t; -*-
 ;;; Commentary:
 ;;; Code:
 

tests/unit/test-webpaste-return-url.el

@@ -1,4 +1,4 @@
-;;; test-webpaste-return-url.el --- Tests for webpaste
+;;; test-webpaste-return-url.el --- Tests for webpaste -*- lexical-binding: t; -*-
 ;;; Commentary:
 ;;; Code:
 

tests/unit/test-webpaste-success-lambdas.el

@@ -1,4 +1,4 @@
-;;; test-webpaste-success-lambdas.el --- Tests for success lambdas
+;;; test-webpaste-success-lambdas.el --- Tests for success lambdas -*- lexical-binding: t; -*-
 ;;; Commentary:
 ;;; Code:
 

tests/unit/test-webpaste.el

@@ -1,4 +1,4 @@
-;;; test-webpaste.el --- Tests for webpaste
+;;; test-webpaste.el --- Tests for webpaste -*- lexical-binding: t; -*-
 ;;; Commentary:
 ;;; Code: