vulkcan: Update SRC_URI to use main branch

The upstream repository has renamed the master branch to main. This
causes fetch errors like:

ERROR: vulkan-loader-1.2.182.0-r0 do_fetch: Fetcher failure: Unable to find revision 1896143df69d439b0933c1bb485f5a4587bdf2dc in branch master even from upstream
ERROR: vulkan-loader-1.2.182.0-r0 do_fetch: Bitbake Fetcher Error: FetchError('Unable to fetch URL from any source.', 'git://github.com/KhronosGroup/Vulkan-Loader.git;protocol=https;branch=master')

Fix it by adding a bbappend replacing 'master' with 'main' in SRC_URI.

Signed-off-by: Nate Drude <nate.d@variscite.com>
(cherry picked from commit 1968354)

recipes-graphics/vulkan/vulkan-loader_%.bbappend

@@ -0,0 +1 @@
+SRC_URI := "${@d.getVar('SRC_URI').replace('branch=master', 'branch=main')}"