[PATCH v3 0/3] t2400: Fix test failures when using grep 2.5

This patchset is in response to build failures on GGG's Cirrus CI freebsd_12 build jobs[1] and was prompted by a discussion thread [2]. These failures seem to be caused by the behavior outlined in [3].

Note: I jumped the gun on v2 a bit as discussions for v1 were still in
progress so these are all changes suggested off v1.

Changes from v2:
  * Split `--sq` change out into separate patch (from 3/3 to 1/3).
  * Convert tab in advice to space to match coding convention and to
    allow regex to be further simplified [4].
  * Simplified regex [4].
  * Reworded commit message for patch 3/3 to better document reason for
    change [4].

1. https://github.com/gitgitgadget/git/pull/1550/checks?check_run_id=14949695859
2. https://lore.kernel.org/git/CALnO6CDryTsguLshcQxx97ZxyY42Twu2hC2y1bLOsS-9zbqXMA@mail.gmail.com/
3. https://stackoverflow.com/questions/4233159/grep-regex-whitespace-behavior
4. https://lore.kernel.org/git/3f3a3f5b-70fd-ec3f-acbb-d585b5eb6cbc@gmail.com/

Jacob Abel (3):
  t2400: drop no-op `--sq` from rev-parse call
  builtin/worktree.c: convert tab in advice to space
  t2400: rewrite regex to avoid unintentional PCRE

 builtin/worktree.c      |  4 ++--
 t/t2400-worktree-add.sh | 12 ++++++------
 2 files changed, 8 insertions(+), 8 deletions(-)

Range-diff against v2:
-:  ---------- > 1:  96c21c5bee t2400: drop no-op `--sq` from rev-parse call
-:  ---------- > 2:  ebfba2d602 builtin/worktree.c: convert tab in advice to space
1:  ef4ebd7350 ! 3:  dee0c8f350 t2400: Fix test failures when using grep 2.5
    @@ Metadata
     Author: Jacob Abel <jacobabel@nullpo.dev>
     
      ## Commit message ##
    -    t2400: Fix test failures when using grep 2.5
    +    t2400: rewrite regex to avoid unintentional PCRE
     
    -    Replace all cases of `\s` with `[[:blank:]]` or ` ` as older versions
    -    of GNU grep (and from what it seems most versions of BSD grep) do not
    -    handle `\s`.
    +    Replace all cases of `\s` with ` ` as it is not part of POSIX BRE or ERE
    +    and therefore not all versions of grep handle it without PCRE support.
     
         For the same reason all cases of `\S` are replaced with `[^ ]`. It's not
    -    an exact replacement (as it does not match tabs) but it is close enough
    -    for this use case.
    -
    -    Replacing `\S` also needs to occur as `\S` is technically PCRE and not
    -    part of ERE even though most modern versions of grep accept it as ERE.
    -
    -    This commit also drops `--sq` from a rev-parse call as it appears to be
    -    a no-op.
    +    an exact replacement but it is close enough for this use case.
     
         Signed-off-by: Jacob Abel <jacobabel@nullpo.dev>
     
    @@ t/t2400-worktree-add.sh: test_wt_add_orphan_hint () {
      		if [ $use_branch -eq 1 ]
      		then
     -			grep -E "^hint:\s+git worktree add --orphan -b \S+ \S+\s*$" actual
    -+			grep -E "^hint:[[:blank:]]+git worktree add --orphan -b [^ ]+ [^ ]+$" actual
    ++			grep -E "^hint:[ ]+git worktree add --orphan -b [^ ]+ [^ ]+$" actual
      		else
     -			grep -E "^hint:\s+git worktree add --orphan \S+\s*$" actual
    -+			grep -E "^hint:[[:blank:]]+git worktree add --orphan [^ ]+$" actual
    ++			grep -E "^hint:[ ]+git worktree add --orphan [^ ]+$" actual
      		fi
      
      	'
    @@ t/t2400-worktree-add.sh: test_dwim_orphan () {
      
      	local git_ns="repo" &&
     @@ t/t2400-worktree-add.sh: test_dwim_orphan () {
    - 					grep "$invalid_ref_regex" actual &&
    - 					! grep "$orphan_hint" actual
    - 				else
    --					headpath=$(git $dashc_args rev-parse --sq --path-format=absolute --git-path HEAD) &&
    -+					headpath=$(git $dashc_args rev-parse --path-format=absolute --git-path HEAD) &&
    + 					headpath=$(git $dashc_args rev-parse --path-format=absolute --git-path HEAD) &&
      					headcontents=$(cat "$headpath") &&
      					grep "HEAD points to an invalid (or orphaned) reference" actual &&
     -					grep "HEAD path:\s*.$headpath." actual &&