fix: Don't restrict length for commit message footer (#467)

<!-- What / Why -->
<!-- Describe the request in detail. What it does and why it's being
changed. -->

Our breaking change footers related to engine changes are often >100
characters, resulting in commitlint CI failures.

<!-- Examples:
  Related to #0
  Depends on #0
  Blocked by #0
  Fixes #0
  Closes #0
-->

Example CI failure:
https://github.com/npm/ssri/actions/runs/10169599799/job/28126863705#step:7:12

Associated PR: npm/ssri#137

.commitlintrc.js

@@ -7,5 +7,6 @@ module.exports = {
     'header-max-length': [2, 'always', 80],
     'subject-case': [0],
     'body-max-line-length': [0],
+    'footer-max-line-length': [0],
   },
 }

lib/content/commitlintrc-js.hbs

@@ -5,5 +5,6 @@ module.exports = {
     'header-max-length': [2, 'always', 80],
     'subject-case': [0],
     'body-max-line-length': [0],
+    'footer-max-line-length': [0],
   },
 }

tap-snapshots/test/apply/source-snapshots.js.test.cjs

@@ -17,6 +17,7 @@ module.exports = {
     'header-max-length': [2, 'always', 80],
     'subject-case': [0],
     'body-max-line-length': [0],
+    'footer-max-line-length': [0],
   },
 }
 
@@ -1455,6 +1456,7 @@ module.exports = {
     'header-max-length': [2, 'always', 80],
     'subject-case': [0],
     'body-max-line-length': [0],
+    'footer-max-line-length': [0],
   },
 }