Remark check: update config and minor tweak

The Remark check is failing (again) for some unfanthomable reason. They must have changed something downstream again.

Let's see if this fixes it.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -59,13 +59,13 @@ Please include as many details as relevant about the environment you experienced
 You should be able to get the version numbers using the `composer info` command.
 -->
 
-| Environment              | Answer
-| ------------------------ | -------
-| PHP version              | x.y.z
-| PHP_CodeSniffer version  | x.y.z
-| PHPCSExtra version       | x.y.z
-| PHPCSUtils version       | x.y.z
-| Install type             | e.g. Composer global, Composer project local, git clone, other (please expand)
+| Environment             | Answer
+| ----------------------- | -------
+| PHP version             | x.y.z
+| PHP_CodeSniffer version | x.y.z
+| PHPCSExtra version      | x.y.z
+| PHPCSUtils version      | x.y.z
+| Install type            | e.g. Composer global, Composer project local, git clone, other (please expand)
 
 
 ## Additional Context (optional)

.remarkrc

@@ -21,7 +21,7 @@
     "remark-lint-no-duplicate-definitions",
     "remark-lint-no-empty-url",
     "remark-lint-no-file-name-consecutive-dashes",
-    "remark-lint-no-file-name-irregular-characters",
+    ["remark-lint-no-file-name-irregular-characters", "\\.a-zA-Z0-9_-"],
     "remark-lint-no-file-name-outer-dashes",
     "remark-lint-no-heading-like-paragraph",
     "remark-lint-no-literal-urls",