Adjust GitHub actions windows build package list

Use the mingw-w64-x86_64 flavour of all packages.  Add curl, so
hfile_libcurl etc. build.  Remove the mingw git package as git
for windows is already present.  Add the location of git for
windows to $PATH.

Switch the badge on README.md from AppVeyor to GitHub.

.github/workflows/windows-build.yml

@@ -15,14 +15,14 @@ jobs:
         msystem: mingw64
         update: false
         install: >-
-          git
-          zlib-devel
-          libbz2-devel
-          liblzma-devel
-          mingw-w64-x86_64-toolchain
           mingw-w64-x86_64-autotools
-          mingw-w64-x86_64-tools-git
+          mingw-w64-x86_64-bzip2
+          mingw-w64-x86_64-curl
           mingw-w64-x86_64-libdeflate
+          mingw-w64-x86_64-toolchain
+          mingw-w64-x86_64-tools-git
+          mingw-w64-x86_64-xz
+          mingw-w64-x86_64-zlib
     - name: Compile htslib
       shell: msys2 {0}
       run: |

README.md

@@ -1,5 +1,5 @@
 [![Build Status](https://api.cirrus-ci.com/github/samtools/htslib.svg?branch=develop)](https://api.cirrus-ci.com/github/samtools/htslib)
-[![Build status](https://ci.appveyor.com/api/projects/status/v46hkwyfjp3l8nd3/branch/develop?svg=true)](https://ci.appveyor.com/project/samtools/htslib/branch/develop)
+[![Build status](https://github.com/samtools/htslib/actions/workflows/windows-build.yml/badge.svg)](https://github.com/samtools/htslib/actions/workflows/windows-build.yml?query=branch%3Adevelop)
 [![Github All Releases](https://img.shields.io/github/downloads/samtools/htslib/total.svg)](https://github.com/samtools/htslib)
 
 HTSlib is an implementation of a unified C library for accessing common file