Fix inject_global_value rules with default value

[jeparlefrancais]

Closes #321

This fixes an issue with how the default value defined in inject_global_value could override the environment value even it was specified.

• add entry to the changelog

[github-actions]

Coverage after merging fix-inject-global-default-value into main will be

87.30%

Coverage Report for Changed Files

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
src/frontend
configuration.rs	87.63%	100%	86.96%	87.75%	142–156, 158–159, 196–200, 59–61, 72–75
work_item.rs	90.29%	100%	90.48%	90.24%	107–109, 150, 155–158
src/process/evaluator
lua_value.rs	93.20%	100%	92.59%	93.33%	153–155, 165–167, 54, 68
src/rules
append_text_comment.rs	81.55%	100%	87.50%	80.92%	102–105, 123–124, 167–172, 201–203, 32–38, 49, 51–54
inject_value.rs	86.75%	100%	93.55%	86.01%	180, 187, 195–204, 206–215, 220–226, 232, 240–242, 74, 78–79
remove_interpolated_string.rs	94.89%	100%	100%	94.38%	209–216
src/rules/convert_require
roblox_index_style.rs	100%	100%	100%	100%