Fix a typo while gathering dependencies from Manifest.toml

[zhubonan]

I got this error while using the 1.7.1 release:

ERROR: type Dict has no field deps
Stacktrace:
 [1] getproperty(x::Dict{Base.UUID, Pkg.Types.PackageEntry}, f::Symbol)
   @ Base ./Base.jl:33
 [2] create_sysimage(packages::Vector{String}; sysimage_path::String, project::String, precompile_execution_file::Vector{String}, precompile_statements_file::Vector{String}, incremental::Bool, filter_stdlibs::Bool, replace_default::Bool, cpu_target::String, script::Nothing, sysimage_build_args::Cmd, include_transitive_dependencies::Bool, base_sysimage::Nothing, isapp::Bool, julia_init_c_file::Nothing, version::Nothing, compat_level::String, soname::Nothing)
   @ PackageCompiler ~/.julia/packages/PackageCompiler/PmmEa/src/PackageCompiler.jl:582

This was probably due to a type to typo as ctx.env.manifest is a Dict.

Perhaps the tests should also be updated?

[zhubonan]

Not sure how to add a test for this.
Maybe it was uncaught because Example package used does not have any dependencies itself?

[codecov]

Codecov Report

Merging #593 (e24d498) into master (1d1b2a2) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #593   +/-   ##
=======================================
  Coverage   84.33%   84.33%           
=======================================
  Files           2        2           
  Lines         498      498           
=======================================
  Hits          420      420           
  Misses         78       78           

Impacted Files	Coverage Δ
src/PackageCompiler.jl	83.73% <100.00%> (ø)

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[KristofferC]

This was probably due to a type to typo as ctx.env.manifest is a Dict.

This is only true on 1.6.1. In 1.6.2 it is of type Pkg.Types.Manifest. However, this PR is also compatible with 1.6.2+ because of

https://github.com/JuliaLang/Pkg.jl/blob/e68aadf6e175228caa512e136caf7f9a4688c3a7/src/Types.jl#L270

So this can be merged and will fix the package on 1.6.1.

And to be explicit, the reason we are not seeing this in CI is that we are testing on 1.6.3.

[zhubonan]

Oh, I see. Thanks for the explanation!
Forgot to mention I was on 1.6.1.