fix(elisp): add lexical-binding comment to all files to suppress new Emacs 31 warnings

I've set `lexical-binding` to `nil` in all Emacs Lisp files to suppress
the warnings introduced in Emacs 31 requiring all elisp files to have a
`lexical-binding` comment.

This retains the default behavior of dynamic binding when no
`lexical-binding` comment is present. With it set to `t` across the
board, various things break, and fixing those is a task for another day.

modules/version-control/siren-code-review.el

@@ -1,4 +1,4 @@
-;;; siren-code-review.el --- jimeh's Emacs Siren: code-review configuration
+;;; siren-code-review.el --- jimeh's Emacs Siren: code-review configuration  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/version-control/siren-diff-hl.el

@@ -1,4 +1,4 @@
-;;; siren-diff-hl.el --- jimeh's Emacs Siren: diff-hl configuration.
+;;; siren-diff-hl.el --- jimeh's Emacs Siren: diff-hl configuration.  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/version-control/siren-ediff.el

@@ -1,4 +1,4 @@
-;;; siren-ediff.el --- jimeh's Emacs Siren: ediff configuration.
+;;; siren-ediff.el --- jimeh's Emacs Siren: ediff configuration.  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/version-control/siren-forge.el

@@ -1,4 +1,4 @@
-;;; siren-forge.el --- jimeh's Emacs Siren: forge configuration
+;;; siren-forge.el --- jimeh's Emacs Siren: forge configuration  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/version-control/siren-gh-notify.el

@@ -1,4 +1,4 @@
-;;; siren-gh-notify.el --- jimeh's Emacs Siren: gh-notify configuration
+;;; siren-gh-notify.el --- jimeh's Emacs Siren: gh-notify configuration  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/version-control/siren-git-gutter.el

@@ -1,4 +1,4 @@
-;;; siren-git-gutter.el --- jimeh's Emacs Siren: git-gutter configuration.
+;;; siren-git-gutter.el --- jimeh's Emacs Siren: git-gutter configuration.  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/version-control/siren-git-timemachine.el

@@ -1,4 +1,4 @@
-;;; siren-git-timemachine.el --- jimeh's Emacs Siren: git-timemachine configuration.
+;;; siren-git-timemachine.el --- jimeh's Emacs Siren: git-timemachine configuration.  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/version-control/siren-github-review.el

@@ -1,4 +1,4 @@
-;;; siren-github-review.el --- jimeh's Emacs Siren: github-review configuration
+;;; siren-github-review.el --- jimeh's Emacs Siren: github-review configuration  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/version-control/siren-github.el

@@ -1,4 +1,4 @@
-;;; siren-github.el --- jimeh's Emacs Siren: Github related stuff.
+;;; siren-github.el --- jimeh's Emacs Siren: Github related stuff.  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/version-control/siren-magit-todos.el

@@ -1,4 +1,4 @@
-;;; siren-magit-todos.el --- jimeh's Emacs Siren: magit-todos configuration
+;;; siren-magit-todos.el --- jimeh's Emacs Siren: magit-todos configuration  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/version-control/siren-magit.el

@@ -1,4 +1,4 @@
-;;; siren-magit.el --- jimeh's Emacs Siren: magit configuration.
+;;; siren-magit.el --- jimeh's Emacs Siren: magit configuration.  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/version-control/siren-magithub.el

@@ -1,4 +1,4 @@
-;;; siren-magithub.el --- jimeh's Emacs Siren: magithub configuration
+;;; siren-magithub.el --- jimeh's Emacs Siren: magithub configuration  -*- lexical-binding: nil; -*-
 
 ;;; Commentary: