docs/policy-reference: add missing ` (open-policy-agent#3617)

Signed-off-by: Stephan Renatus <[email protected]>

docs/content/policy-reference.md

@@ -364,7 +364,7 @@ complex types.
 | Built-in | Description | Wasm Support |
 | ------- |-------------|---------------|
 | <span class="opa-keep-it-together">``output := regex.match(pattern, value)``</span> | ``output`` is a ``boolean`` that indicates if ``value`` matches the regex ``pattern``. | ✅ |
-| <span class="opa-keep-it-together">``output := regex.is_valid(pattern)``</span> | ``output`` is a ``boolean`` that indicates if ``pattern` is a valid regex pattern. The detailed syntax for regex patterns is defined by https://github.com/google/re2/wiki/Syntax. | ✅ |
+| <span class="opa-keep-it-together">``output := regex.is_valid(pattern)``</span> | ``output`` is a ``boolean`` that indicates if ``pattern`` is a valid regex pattern. The detailed syntax for regex patterns is defined by https://github.com/google/re2/wiki/Syntax. | ✅ |
 | <span class="opa-keep-it-together">``output := regex.split(pattern, string)``</span> | ``output`` is ``array[string]`` representing elements of ``string`` separated by ``pattern`` | ``SDK-dependent`` |
 | <span class="opa-keep-it-together">``regex.globs_match(glob1, glob2)``</span> | true if the intersection of regex-style globs ``glob1`` and ``glob2`` matches a non-empty set of non-empty strings. The set of regex symbols is limited for this builtin: only ``.``, ``*``, ``+``, ``[``, ``-``, ``]`` and ``\`` are treated as special symbols. | ``SDK-dependent`` |
 | <span class="opa-keep-it-normal">``output := regex.template_match(pattern, string, delimiter_start, delimiter_end)``</span> | ``output`` is true if ``string`` matches ``pattern``. ``pattern`` is a string containing ``0..n`` regular expressions delimited by ``delimiter_start`` and ``delimiter_end``. Example ``regex.template_match("urn:foo:{.*}", "urn:foo:bar:baz", "{", "}")`` returns ``true``. | ``SDK-dependent`` |