Set SemverCompatible to false for Conan packages (#21275)

Fixes #21250
Related #20414

Conan packages don't have to follow SemVer.
The migration fixes the setting for all existing Conan and Generic
(#20414) packages.

tests/integration/api_packages_conan_test.go

@@ -267,7 +267,7 @@ func TestPackageConan(t *testing.T) {
 
 				pd, err := packages.GetPackageDescriptor(db.DefaultContext, pvs[0])
 				assert.NoError(t, err)
-				assert.NotNil(t, pd.SemVer)
+				assert.Nil(t, pd.SemVer)
 				assert.Equal(t, name, pd.Package.Name)
 				assert.Equal(t, version1, pd.Version.Version)
 				assert.IsType(t, &conan_module.Metadata{}, pd.Metadata)