Fix XML mime type - Githubissues

This is verified at staging-schemas.isotc211.org as follows:

$ curl -v https://staging-schemas.isotc211.org/19139/-/gmx/1.0/gmx.xsd
*   Trying 65.9.86.69:443...
* Connected to staging-schemas.isotc211.org (65.9.86.69) port 443 (#0)
* ALPN, offering h2
* ALPN, offering http/1.1
* successfully set certificate verify locations:
*  CAfile: /etc/ssl/cert.pem
*  CApath: none
* (304) (OUT), TLS handshake, Client hello (1):
* (304) (IN), TLS handshake, Server hello (2):
* (304) (IN), TLS handshake, Unknown (8):
* (304) (IN), TLS handshake, Certificate (11):
* (304) (IN), TLS handshake, CERT verify (15):
* (304) (IN), TLS handshake, Finished (20):
* (304) (OUT), TLS handshake, Finished (20):
* SSL connection using TLSv1.3 / AEAD-AES128-GCM-SHA256
* ALPN, server accepted to use h2
* Server certificate:
*  subject: CN=staging-schemas.isotc211.org
*  start date: Aug 20 00:00:00 2022 GMT
*  expire date: Sep 18 23:59:59 2023 GMT
*  subjectAltName: host "staging-schemas.isotc211.org" matched cert's "staging-schemas.isotc211.org"
*  issuer: C=US; O=Amazon; OU=Server CA 1B; CN=Amazon
*  SSL certificate verify ok.
* Using HTTP2, server supports multiplexing
* Connection state changed (HTTP/2 confirmed)
* Copying HTTP/2 data in stream buffer to connection buffer after upgrade: len=0
* Using Stream ID: 1 (easy handle 0x14200d000)
> GET /19139/-/gmx/1.0/gmx.xsd HTTP/2
> Host: staging-schemas.isotc211.org
> user-agent: curl/7.79.1
> accept: */*
> 
* Connection state changed (MAX_CONCURRENT_STREAMS == 128)!
< HTTP/2 200 
< content-type: application/xml
< content-length: 1171
< date: Wed, 01 Feb 2023 07:01:44 GMT
< last-modified: Mon, 01 Feb 2021 14:01:45 GMT
< etag: "19f65f312a4ed74ac83512cc6536c995"
< server: AmazonS3
< vary: Accept-Encoding
< x-cache: Miss from cloudfront
< via: 1.1 a06d82f018833bef3e7f2e9fd230e5ee.cloudfront.net (CloudFront)
< x-amz-cf-pop: AMS1-C1
< x-amz-cf-id: _sgbAOuYK4hBg17Hj4dQrFqv9PNWVNCY9yxHSgoNTOOeubpOSoGo8w==
< 
<?xml   version="1.0" encoding="utf-8"?>
<xs:schema
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    xmlns:xlink="http://www.w3.org/1999/xlink"
    xmlns:gmx="http://www.isotc211.org/2005/gmx"
    targetNamespace="http://www.isotc211.org/2005/gmx"
    elementFormDefault="qualified"
    version="2012-07-13">
    <!-- ================================= Annotation ================================ -->
    <xs:annotation>
        <xs:documentation>Geographic Metadata XML  (GMX) Schema is a component of the XML  Schema Implementation of Geographic Information Metadata documented in ISO/TS 19139:2007. GMX includes all the definitions of http://www.isotc211.org/2005/gmx namespace. The root document of this namespace is the file gmx.xsd.</xs:documentation>
    </xs:annotation>
    <!-- ================================== Imports ================================== -->
    <xs:include schemaLocation="gmxUsage.xsd"/>
    <!-- ########################################################################### -->
    <!-- ########################################################################### -->
    <!-- ================================== Classes ================================= -->
</xs:schema>
* Connection #0 to host staging-schemas.isotc211.org left intact

It says:

< content-type: application/xml

ISO-TC211 / schemas-isotc211.github.io

Fix XML mime type #34