Do not self-host shields.io badges in the documentation

The privacy plugin downloads img.shields.io badges at build time; when
shields.io times out, mkdocs build --strict aborts and the
ci_test_build_documentation job fails until it is restarted. Exclude
the host like repology.org; the version badges stay current this way.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/docs/api/basic_json/operator_eq.md

@@ -11,12 +11,10 @@ template<typename ScalarType>
 bool operator==(ScalarType lhs, const const_reference rhs) noexcept(/* see below */); // (2)
 
 // since C++20
-class basic_json {
-    bool operator==(const_reference rhs) const noexcept;              // (1)
+bool operator==(const_reference rhs) const noexcept;             // (1)
 
-    template<typename ScalarType>
-    bool operator==(ScalarType rhs) const noexcept(/* see below */); // (2)
-};
+template<typename ScalarType>
+bool operator==(ScalarType rhs) const noexcept(/* see below */); // (2)
 ```
 
 1. Compares two JSON values for equality according to the following rules:

docs/mkdocs/docs/api/basic_json/operator_spaceship.md

@@ -2,12 +2,10 @@
 
 ```cpp
 // since C++20
-class basic_json {
-    std::partial_ordering operator<=>(const_reference rhs) const noexcept;  // (1)
+std::partial_ordering operator<=>(const_reference rhs) const noexcept;                   // (1)
 
-    template<typename ScalarType>
-    std::partial_ordering operator<=>(const ScalarType rhs) const noexcept(/* see below */); // (2)
-};
+template<typename ScalarType>
+std::partial_ordering operator<=>(const ScalarType rhs) const noexcept(/* see below */); // (2)
 ```
 
 1. 3-way compares two JSON values producing a result of type `std::partial_ordering` according to the following rules:

docs/mkdocs/docs/api/json_pointer/operator_eq.md

@@ -18,13 +18,11 @@ bool operator==(
     const json_pointer<RefStringTypeRhs>& rhs);                     // (2)
 
 // since C++20
-class json_pointer {
-    template<typename RefStringTypeRhs>
-    bool operator==(
-        const json_pointer<RefStringTypeRhs>& rhs) const noexcept;  // (1)
+template<typename RefStringTypeRhs>
+bool operator==(
+    const json_pointer<RefStringTypeRhs>& rhs) const noexcept;      // (1)
 
-    bool operator==(const string_t& rhs) const;                     // (2)
-};
+bool operator==(const string_t& rhs) const;                         // (2)
 ```
 
 1. Compares two JSON pointers for equality by comparing their reference tokens.

docs/mkdocs/docs/api/json_pointer/operator_spaceship.md

@@ -2,10 +2,8 @@
 
 ```cpp
 // since C++20
-class json_pointer {
-    template<typename RefStringTypeRhs>
-    std::strong_ordering operator<=>(const json_pointer<RefStringTypeRhs>& rhs) const noexcept; // *NOPAD*
-};
+template<typename RefStringTypeRhs>
+std::strong_ordering operator<=>(const json_pointer<RefStringTypeRhs>& rhs) const noexcept; // *NOPAD*
 ```
 
 3-way compares two JSON pointers by lexicographically comparing their sequences of reference tokens: corresponding

docs/mkdocs/mkdocs.yml

@@ -453,8 +453,12 @@ plugins:
       # package badges (the fetch fails, then reading the missing cache entry
       # raises FileNotFoundError). Readers' browsers are served normally, so
       # leave these badges as external references instead of self-hosting them.
+      # The same goes for img.shields.io, whose version badges time out from
+      # time to time (strict mode turns the failed download into an error) and
+      # would go stale between builds if they were self-hosted anyway.
       assets_exclude:
         - repology.org/*
+        - img.shields.io/*
   - llmstxt:
       markdown_description: >
         JSON for Modern C++ is a C++11 header-only library implementing a JSON