cmd/gist-logs: On 404, the PAT probably needs more permissions

- This 404 error is from GitHub, and GitHub doesn't give us any more
  informations about scopes for the gist endpoint (for some reason). But we can
  safely assume, as it happens a lot, that "Error: Not Found" (404) is because
  the user hasn't granted their `HOMEBREW_GITHUB_API_TOKEN` the `gist` scope.

Before:

```shell
$ HOMEBREW_GITHUB_API_TOKEN=<token_without_gist_scope> brew gist-logs -p logrotate
Error: Not Found
```

After:

```shell
❯ HOMEBREW_GITHUB_API_TOKEN=<token_without_gist_scope> brew gist-logs logrotate
Error: Your GitHub API token likely doesn't have the `gist` scope.
Create a GitHub personal access token:
https://github.com/settings/tokens/new?scopes=gist&description=Homebrew
echo 'export HOMEBREW_GITHUB_API_TOKEN=your_token_here' >> ~/.zshrc
```

Library/Homebrew/cmd/gist-logs.rb

@@ -63,7 +63,15 @@ module Homebrew
     else
       "#{f.name} (#{f.full_name}) on #{OS_VERSION} - Homebrew build logs"
     end
-    url = GitHub.create_gist(files, descr, private: args.private?)
+
+    begin
+      url = GitHub.create_gist(files, descr, private: args.private?)
+    rescue GitHub::API::HTTPNotFoundError
+      odie <<~EOS
+        Your GitHub API token likely doesn't have the `gist` scope.
+        #{GitHub.pat_blurb(GitHub::CREATE_GIST_SCOPES)}
+      EOS
+    end
 
     url = GitHub.create_issue(f.tap, "#{f.name} failed to build on #{MacOS.full_version}", url) if args.new_issue?
 

Library/Homebrew/utils/github/api.rb

@@ -5,7 +5,18 @@ require "tempfile"
 require "utils/shell"
 require "utils/formatter"
 
+# A module that interfaces with GitHub, code like PAT scopes, credential handling and API errors.
 module GitHub
+  def self.pat_blurb(scopes = ALL_SCOPES)
+    <<~EOS
+      Create a GitHub personal access token:
+      #{Formatter.url(
+        "https://github.com/settings/tokens/new?scopes=#{scopes.join(",")}&description=Homebrew",
+      )}
+      #{Utils::Shell.set_variable_in_profile("HOMEBREW_GITHUB_API_TOKEN", "your_token_here")}
+    EOS
+  end
+
   API_URL = "https://api.github.com"
   API_MAX_PAGES = 50
   API_MAX_ITEMS = 5000
@@ -14,14 +25,6 @@ module GitHub
   CREATE_ISSUE_FORK_OR_PR_SCOPES = ["repo"].freeze
   CREATE_WORKFLOW_SCOPES = ["workflow"].freeze
   ALL_SCOPES = (CREATE_GIST_SCOPES + CREATE_ISSUE_FORK_OR_PR_SCOPES + CREATE_WORKFLOW_SCOPES).freeze
-  ALL_SCOPES_URL = Formatter.url(
-    "https://github.com/settings/tokens/new?scopes=#{ALL_SCOPES.join(",")}&description=Homebrew",
-  ).freeze
-  CREATE_GITHUB_PAT_MESSAGE = <<~EOS
-    Create a GitHub personal access token:
-        #{ALL_SCOPES_URL}
-      #{Utils::Shell.set_variable_in_profile("HOMEBREW_GITHUB_API_TOKEN", "your_token_here")}
-  EOS
   GITHUB_PERSONAL_ACCESS_TOKEN_REGEX = /^(?:[a-f0-9]{40}|gh[po]_\w{36,251})$/.freeze
 
   # Helper functions to access the GitHub API.
@@ -49,7 +52,7 @@ module GitHub
     class RateLimitExceededError < Error
       def initialize(reset, github_message)
         @github_message = github_message
-        new_pat_message = ", or:\n#{CREATE_GITHUB_PAT_MESSAGE}" if API.credentials.blank?
+        new_pat_message = ", or:\n#{pat_blurb}" if API.credentials.blank?
         super <<~EOS
           GitHub API Error: #{github_message}
           Try again in #{pretty_ratelimit_reset(reset)}#{new_pat_message}
@@ -76,7 +79,7 @@ module GitHub
             The GitHub credentials in the macOS keychain may be invalid.
             Clear them with:
               printf "protocol=https\\nhost=github.com\\n" | git credential-osxkeychain erase
-            #{CREATE_GITHUB_PAT_MESSAGE}
+            #{pat_blurb}
           EOS
         end
         super message.freeze
@@ -87,7 +90,7 @@ module GitHub
     class MissingAuthenticationError < Error
       def initialize
         message = +"No GitHub credentials found in macOS Keychain or environment.\n"
-        message << CREATE_GITHUB_PAT_MESSAGE
+        message << pat_blurb
         super message
       end
     end
@@ -177,7 +180,7 @@ module GitHub
         Your #{what} credentials do not have sufficient scope!
         Scopes required: #{needed_scopes}
         Scopes present:  #{credentials_scopes}
-        #{CREATE_GITHUB_PAT_MESSAGE}
+        #{pat_blurb}
       EOS
     end