[BUG] `orchestrion pin` on clean repo breaks in `pruneImports` with vendoring

[RomainMuller]

Version of orchestrion
1.5.0

Describe what happened:
A Dockerfile with these characteristics:

# ...

ARG CGO
ARG OS
ARG ARCH
RUN mkdir /go/src/project
WORKDIR /go/src/project
COPY . ./
RUN go install github.com/DataDog/orchestrion@latest
RUN orchestrion pin
RUN go env
RUN echo "CGO = "$CGO
RUN echo "OS = "$OS
RUN echo "ARCH = "$ARCH
RUN CGO_ENABLED=$CGO GOOS=$OS GOARCH=$ARCH govvv build -mod vendor -toolexec='orchestrion toolexec' -a -installsuffix cgo -ldflags '-extldflags "-static"' -o ./bin/project ./cmd/project/project.go
RUN cp ./bin/project /bin/
RUN CGO_ENABLED=$CGO GOOS=$OS GOARCH=$ARCH govvv build -mod vendor -toolexec='orchestrion toolexec' -a -installsuffix cgo -ldflags '-extldflags "-static"' -o ./bin/projectcli ./cmd/projectcli/projectcli.go
RUN cp ./bin/projectcli /bin/

Results in the following error:

ERROR [project builder 6/14] RUN orchestrion pin 0.3s
------
> [project builder 6/14] RUN orchestrion pin:
0.258 pruning imports from "/go/src/project/orchestrion.tool.go": pruneImports: err: exit status 1: stderr: go: inconsistent vendoring in /go/src/project:
0.258 github.com/DataDog/dd-trace-go/orchestrion/all/v2@v2.2.2: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt
0.258 github.com/DataDog/orchestrion@v1.5.0: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt
[...]
0.258 To ignore the vendor directory, use -mod=readonly or -mod=mod.
0.258 To sync the vendor directory, run:
0.258 go mod vendor
0.258
------
failed to solve: process "/bin/sh -c orchestrion pin" did not complete successfully: exit code: 255
make: *** [Makefile: 14 :  build] Error 17

Describe what you expected:

Expected go mod vendor to be automatically run at the right time in the process so this error does not occur.