Merge #1043: build: add --strict_front_matter to build invocation

f703571 build: add --strict_front_matter to build invocation (fanquake)

Pull request description:

  Should help catch issues like those in #1042, which didn't cause the CI to fail.

  ```bash
  bundle exec jekyll server --future --drafts --unpublished --incremental --strict_front_matter
  ...
   Incremental build: enabled
        Generating...
               Error: YAML Exception reading /bitcoincore.org/_posts/en/posts/2024-06-10-disclose-bip70-crash.md: (<unknown>): mapping values are not allowed in this context at line 2 column 18
                      ------------------------------------------------
  ```

ACKs for top commit:
  dergoegge:
    utACK f703571

Tree-SHA512: f9e748ca356cac1043ce0458cd654eb041f446a10861b38d608b28c1fbb7f079bdf3bb2b9f06b0e37a962bf26d35563bf59a538deaf18ffe98b859ffb5cd6f97

Author: fanquake

Makefile

@@ -2,11 +2,11 @@ all: build test
 
 preview:
 	bundle exec jekyll clean
-	bundle exec jekyll serve --future --drafts --unpublished --incremental
+	bundle exec jekyll serve --future --drafts --unpublished --incremental --strict_front_matter
 
 build:
 	bundle exec jekyll clean
-	bundle exec jekyll build --future --drafts --unpublished
+	bundle exec jekyll build --future --drafts --unpublished --strict_front_matter
 
 test: test-fast test-slow