misc: typo and grammar fixes

- Replace `Github` with `GitHub`.
- Replace `windows` with `Windows`
- Replace `advice` with `advise` where a verb is used.
- A few fixes on removing repeated words.
- Replace `a HTTP` with `an HTTP`

Closes #9802

lib/http2.c

@@ -109,7 +109,7 @@ static int http2_getsock(struct Curl_easy *data,
   sock[0] = conn->sock[FIRSTSOCKET];
 
   if(!(k->keepon & KEEP_RECV_PAUSE))
-    /* Unless paused - in a HTTP/2 connection we can basically always get a
+    /* Unless paused - in an HTTP/2 connection we can basically always get a
        frame so we should always be ready for one */
     bitmap |= GETSOCK_READSOCK(FIRSTSOCKET);
 
@@ -1120,7 +1120,7 @@ static int on_header(nghttp2_session *session, const nghttp2_frame *frame,
 
   /* nghttp2 guarantees that namelen > 0, and :status was already
      received, and this is not pseudo-header field . */
-  /* convert to a HTTP1-style header */
+  /* convert to an HTTP1-style header */
   result = Curl_dyn_addn(&stream->header_recvbuf, name, namelen);
   if(result)
     return NGHTTP2_ERR_CALLBACK_FAILURE;
@@ -1351,7 +1351,7 @@ static CURLcode http2_init(struct Curl_easy *data, struct connectdata *conn)
 }
 
 /*
- * Append headers to ask for a HTTP1.1 to HTTP2 upgrade.
+ * Append headers to ask for an HTTP1.1 to HTTP2 upgrade.
  */
 CURLcode Curl_http2_request_upgrade(struct dynbuf *req,
                                     struct Curl_easy *data)
@@ -2307,7 +2307,7 @@ void Curl_http2_cleanup_dependencies(struct Curl_easy *data)
     Curl_http2_remove_child(data->set.stream_depends_on, data);
 }
 
-/* Only call this function for a transfer that already got a HTTP/2
+/* Only call this function for a transfer that already got an HTTP/2
    CURLE_HTTP2_STREAM error! */
 bool Curl_h2_http_1_1_error(struct Curl_easy *data)
 {