scripted-diff: Use std::span over Span

-BEGIN VERIFY SCRIPT-

 ren() { sed -i "s!\<$1\>!$2!g" $( git grep -l "$1" -- "./src" ":(exclude)src/span.h" ":(exclude)src/leveldb/db/log_test.cc" ) ; }

 ren Span            std::span
 ren AsBytes         std::as_bytes
 ren AsWritableBytes std::as_writable_bytes

 sed -i 's!SpanPopBack(Span!SpanPopBack(std::span!g' ./src/span.h

-END VERIFY SCRIPT-

src/script/miniscript.cpp

@@ -419,7 +419,7 @@ std::optional<int64_t> ParseScriptNumber(const Opcode& in) {
     return {};
 }
 
-int FindNextChar(Span<const char> sp, const char m)
+int FindNextChar(std::span<const char> sp, const char m)
 {
     for (int i = 0; i < (int)sp.size(); ++i) {
         if (sp[i] == m) return i;