internal/e2e: tweak expected error string after the cue/load changes

https://cuelang.org/cl/1175995 switched cue/load to modpkgload
to resolve module dependencies, which shouldn't have broken any users,
but did break the end-to-end tests as they looked for a particular
error string match. That error message changed slightly:

    # Double check that cmd/cue cannot download the dependency either. (0.694s)
    > env-fill cue.mod/module.cue out_foo.cue
    > ! exec cue export
    [stderr]
    import failed: cannot find package "github.com/cue-labs-modules-testing/e2e-github_app_private-2024.01.25-15.11.20-e632f1@v0": cannot fetch github.com/cue-labs-modules-testing/e2e-github_app_private-2024.01.25-15.11.20-e632f1@v0.0.1: module github.com/cue-labs-modules-testing/e2e-github_app_private-2024.01.25-15.11.20-e632f1@v0.0.1: module not found:
        ./out_foo.cue:3:8
    [exit status 1]
    > stderr 'cannot resolve dependencies'
    FAIL: testdata/script/github_app_private.txtar:39: no match for `cannot resolve dependencies` found in stderr

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: I33c02c36bc87c171791fa89564eb05402b0336aa
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1176006
Reviewed-by: Roger Peppe <rogpeppe@gmail.com>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>

internal/e2e/testdata/script/github_app_private.txtar

@@ -36,7 +36,7 @@ cd ../depend
 # Double check that cmd/cue cannot download the dependency either.
 env-fill cue.mod/module.cue out_foo.cue
 ! exec cue export
-stderr 'cannot resolve dependencies'
+stderr 'cannot find package.*module not found'
 
 -- publish/cue.mod/module.cue --
 module: "${MODVER}"