Replace invalid tag characters for master images

Signed-off-by: Ben Reedy <breed808@breed808.com>

.github/workflows/ci.yml

@@ -144,6 +144,8 @@ jobs:
           goversioninfo.exe -ver-major $VersionParts[0] -ver-minor $VersionParts[1] -ver-patch $VersionParts[2] -product-version $Version -platform-specific
 
           make crossbuild
+          # '+' symbols are invalid characters in image tags
+          (Get-Content -Path VERSION) -replace '\+', '_' | Set-Content -Path VERSION
           make build-all
           # GH requires all files to have different names, so add version/arch to differentiate
           foreach($Arch in "amd64","386") {