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

src/tool_operate.c

@@ -730,7 +730,7 @@ static CURLcode single_transfer(struct GlobalConfig *global,
   if(config->postfields) {
     if(config->use_httpget) {
       if(!httpgetfields) {
-        /* Use the postfields data for a http get */
+        /* Use the postfields data for an HTTP get */
         httpgetfields = state->httpgetfields = strdup(config->postfields);
         Curl_safefree(config->postfields);
         if(!httpgetfields) {

src/tool_urlglob.c

@@ -350,7 +350,7 @@ static bool peek_ipv6(const char *str, size_t *skip)
   memcpy(hostname, str, hlen);
   hostname[hlen] = 0;
 
-  /* ask to "guess scheme" as then it works without a https:// prefix */
+  /* ask to "guess scheme" as then it works without an https:// prefix */
   rc = curl_url_set(u, CURLUPART_URL, hostname, CURLU_GUESS_SCHEME);
 
   curl_url_cleanup(u);