Fix module-based build

@lpgeneau reports that module-based build fails with

    2021-07-07 16:37:34 slapos[2415] INFO GOMODSRC /srv/slapgrid/slappart11/srv/runner/software/a12cdf3481c4202ae72cb255d8a6c183/go.work/src/lab.nexedi.com/kirr/git-backup:./...
    2021-07-07 16:37:34 slapos[2415] INFO ../../../../pkg/mod/lab.nexedi.com/kirr/go123@v0.0.0-20210302025843-863c4602a230/xerr/xerr.go:77:2: missing go.sum entry for module providing package github.com/pkg/errors (imported by lab.nexedi.com/kirr/go123/xerr); to add:
    2021-07-07 16:37:34 slapos[2415] INFO   go get lab.nexedi.com/kirr/go123/xerr@v0.0.0-20210302025843-863c4602a230
    2021-07-07 16:37:34 slapos[2415] INFO gowork.goinstall: Non zero exit code (1) while running command.

-> Fix it by updating go123 dependency and running recommended command to update go.sum.

Amends 3c804105 (*: Add Go modules support; Upgrade to latest git2go release)

go.mod

@@ -4,5 +4,5 @@ go 1.14
 
 require (
 	github.com/libgit2/git2go/v31 v31.4.12
-	lab.nexedi.com/kirr/go123 v0.0.0-20210302025843-863c4602a230
+	lab.nexedi.com/kirr/go123 v0.0.0-20210701064927-df4b66e6ee66
 )

go.sum

@@ -5,6 +5,7 @@ github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510/go.mod h1:pupxD2MaaD3
 github.com/kylelemons/godebug v1.1.0/go.mod h1:9/0rRGxNHcop5bhtWyNeEfOS8JIWk580+fNqagV/RAw=
 github.com/libgit2/git2go/v31 v31.4.12 h1:+/8GzvoEKXzpeFeidTwcKcZNFGm7VaowgNzRduRehMc=
 github.com/libgit2/git2go/v31 v31.4.12/go.mod h1:c/rkJcBcUFx6wHaT++UwNpKvIsmPNqCeQ/vzO4DrEec=
+github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
 github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/yuin/goldmark v1.2.1/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
@@ -40,3 +41,5 @@ golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8T
 golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 lab.nexedi.com/kirr/go123 v0.0.0-20210302025843-863c4602a230 h1:Ca6y0vXtxL2ncrg6rXL35FkXaqc2QWvctNSeZFGObZ8=
 lab.nexedi.com/kirr/go123 v0.0.0-20210302025843-863c4602a230/go.mod h1:pwDpdCuvtz0QxisDzV/z9eUb9zc/rMQec520h4i8VWQ=
+lab.nexedi.com/kirr/go123 v0.0.0-20210701064927-df4b66e6ee66 h1:+4bR6/oPsEboLSD3+69cFZPQrjr8RGuKwToD/DKlg54=
+lab.nexedi.com/kirr/go123 v0.0.0-20210701064927-df4b66e6ee66/go.mod h1:pwDpdCuvtz0QxisDzV/z9eUb9zc/rMQec520h4i8VWQ=