Rework future tense in user-facing messages

[lucperkins]

Motivation

There's a tendency that a lot of us have when writing English to use a kind of "fake" future tense to express regular or expected connections between things. In general, though, it's better to reserve the future tense for things that will happen in the future and use simple present tense to express "if x then y"-style connections. Changes correspond to this PR.

[cole-h]

FYI, CI is failing because you missed updating the wording in a test. Here's a diff fixing that.

diff --git a/tests/functional/fetchGitShallow.sh b/tests/functional/fetchGitShallow.sh
index cf7e5fd4fb..4c21bd7ac8 100644
--- a/tests/functional/fetchGitShallow.sh
+++ b/tests/functional/fetchGitShallow.sh
@@ -43,7 +43,7 @@
 [[ $(nix eval --impure --expr "(builtins.fetchTree { type = \"git\"; url = \"file://$TEST_ROOT/shallow-clone\"; ref = \"dev\"; shallow = true; }).revCount or 123") == 123 ]]
 
 # Test 3: Check unlocked input error message
-expectStderr 1 nix eval --expr 'builtins.fetchTree { type = "git"; url = "file:///foo"; }' | grepQuiet "'fetchTree' will not fetch unlocked input"
+expectStderr 1 nix eval --expr 'builtins.fetchTree { type = "git"; url = "file:///foo"; }' | grepQuiet "'fetchTree' doesn't fetch unlocked input"
 
 # Test 4: Regression test for revCount in worktrees derived from shallow clones
 # Add a worktree to the shallow clone

[roberth]

Thanks!