Disable cover on special blocks

Three blocks of code had to be marked no cover. Those blocks are entered and tested
but coverage reports them as missing. It might be due to the decorator…
I've tried to simplify the code leading to it but could fix the missing lines…

Once we merge this, I'll open a ticket to revisit this in the future.

Author: rgaudin

src/zimscraperlib/rewriting/html.py

@@ -560,7 +560,7 @@ def rewrite_meta_charset_content(
         return
     if attr_name == "charset":
         return (attr_name, "UTF-8")
-    if attr_name == "content" and any(
+    if attr_name == "content" and any(  # pragma: no coverage (coverage bug)
         attr_name.lower() == "http-equiv"
         and attr_value
         and attr_value.lower() == "content-type"
@@ -574,7 +574,9 @@ def rewrite_onxxx_tags(
     attr_name: str, attr_value: str | None, js_rewriter: JsRewriter
 ) -> AttrNameAndValue | None:
     """Rewrite onxxx script attributes"""
-    if attr_value and attr_name.startswith("on") and not attr_name.startswith("on-"):
+    if (
+        attr_value and attr_name.startswith("on") and not attr_name.startswith("on-")
+    ):  # pragma: no coverage (coverage bug)
         return (attr_name, js_rewriter.rewrite(attr_value))
 
 
@@ -583,7 +585,7 @@ def rewrite_style_tags(
     attr_name: str, attr_value: str | None, css_rewriter: CssRewriter
 ) -> AttrNameAndValue | None:
     """Rewrite style attributes"""
-    if attr_value and attr_name == "style":
+    if attr_value and attr_name == "style":  # pragma: no coverage (coverage bug)
         return (attr_name, css_rewriter.rewrite_inline(attr_value))