fix(server): use case-insensitive comparison for Expect: 100-continue (#2709)

According to rfc2616#section-14.20 the header value is case-insensitive. Certain clients send the expectation as `100-Continue` and this should be handled by the server.

Closes #2708

src/proto/h1/role.rs

@@ -271,7 +271,10 @@ impl Http1Transaction for Server {
                     }
                 }
                 header::EXPECT => {
-                    expect_continue = value.as_bytes() == b"100-continue";
+                    // According to https://datatracker.ietf.org/doc/html/rfc2616#section-14.20
+                    // Comparison of expectation values is case-insensitive for unquoted tokens
+                    // (including the 100-continue token)
+                    expect_continue = value.as_bytes().eq_ignore_ascii_case(b"100-continue");
                 }
                 header::UPGRADE => {
                     // Upgrades are only allowed with HTTP/1.1